- this is consistent with compiler defaults, and helps Darwin users

- tie the MPI rules to the base compiler type *without* its version.
  Eg, linux64Gcc (which exists) instead of linux64Gcc81

- improvement documentation for surface sampling.

- can now specify alternative sampling scheme for obtaining the
  face values instead of just using the "cell" value. For example,

      sampleScheme    cellPoint;

  This can be useful for cases when the surface is close to a boundary
  cell and there are large gradients in the sampled field.

- distanceSurface now handles non-closed surfaces more robustly.
  Unknown regions (not inside or outside) are marked internally and
  excluded from consideration. This allows use of 'signed' surfaces
  where not previously possible.

- since PackedBoolList is now a compatibility typedef for bitSet,
  it is useful to have an additional means of distinction.

STYLE: simplify internal version tests and compiler defines.

- the API version is now conveyed via the OPENFOAM define directly.
  The older OPENFOAM_PLUS define is provided for existing code.

- parsing error state only arises from a missing final newline
  in the file (which the dnl macro does not capture).
  Report with a warning instead of modifying the dnl macro since
  we generally wish to know about this anyhow.

- add missing newline to YEqn.H file.

- handling of dead links (find -L -delete unsupported)

- remove ignore case flag on 's/../../i' used in have_scotch script.
  It is unneeded and not tolerated by Darwin's sed.

- avoid embedded comments in EXE_INC (Make/options files), which do
  not work well with the OSX LLVM cpp.
  It strips out the comments but also removes the continuation char.

STYLE: adjust notes about paraview library locations

- was somewhat redundant in wmake/rules/General/general anyhow

- generalize some of the library extensions (.so vs .dylib).
  Provide as wmake 'sysFunctions'

- added note about unsupported/incomplete system support

- centralize detection of ThirdParty packages into wmake/ subdirectory
  by providing a series of scripts in the spirit of GNU autoconfig.
  For example,

      have_boost, have_readline, have_scotch, ...

  Each of the `have_<package>` scripts will generally provide the
  following type of functions:

      have_<package>          # detection
      no_<package>            # reset
      echo_<package>          # echoing

  and the following type of variables:

      HAVE_<package>          # unset or 'true'
      <package>_ARCH_PATH     # root for <package>
      <package>_INC_DIR       # include directory for <package>
      <package>_LIB_DIR       # library directory for <package>

  This simplifies the calling scripts:

      if have_metis
      then
          wmake metisDecomp
      fi

  As well as reducing clutter in the corresponding Make/options:

      EXE_INC = \
          -I$(METIS_INC_DIR) \
          -I../decompositionMethods/lnInclude

      LIB_LIBS = \
          -L$(METIS_LIB_DIR) -lmetis

  Any additional modifications (platform-specific or for an external build
  system) can now be made centrally.

- permits platform-specific override of the general CGAL rules

- the previous grammar used

      '/*' { fgoto comment; }

  to start processing multi-line comments and

      comment := any* :>> '*/' @{ fgoto main; };

  as a finishing action to return to normal lexing, but seemed not to
  have been triggered properly.

  Now simply trap in a single rule:

      '/*' any* :>> '*/';             # Multi-line comment

STYLE: use more compact dnl (delete to newline)

  OLD:   [^\n]* '\n'
  NEW:   (any* -- '\n') '\n'

  eliminates the intermediate state

- adjusted grammar to be more precise

- However, the new ragel-based parser is much faster
  than the others, and does not cause 'too many open files' error
  that the flex-based parser does (issue #784).

  The timings (using src/sampling as being somewhat representative)

    $ wclean; wmakeLnInclude -u .; time wmake -s dep

        3.4s  wmkdepend (ragel) [now default]
        5.7s  wmkdep (flex)
        6.1s  cpp -M

- The makeDepend script is for testing purposes only, but could used as
  a hook for other dependency generation systems (eg, ninja).
  It simply wraps 'cpp -M' in a form that is calling compatible with
  wmkdepend.

BUG: wmkdepend parser was missing optional leading space on #include match

STYLE: use -G2 (goto-based) option for wmkdepend state machine

- the machine is compact with few states and lends itself to this

- a partial selection from https://github.com/mrklein/openfoam-os-x
  with adjustments. The primary purpose is to reduce header-level
  incompatibilities and to provide a common set of make rules to allow
  easier patching (or re-integration).

  This is similar to efforts (Feb 2010) but using ragel
  (https://en.wikipedia.org/wiki/Ragel) instead of the now defunct
  coco/r. The modified commit message from 2010:

ENH: add C++-based wmkdepend parser (uses ragel grammar).

- This avoids dependency on lex/flex and provides better encapsulation
  for buffer switching. As a result, the maximum number of open files
  only corresponds to the include depth.

--

Note that the flex source and rules are still available, but are not
deactivate (see wmake/rules/General/transform)

- less efficient and less portable than using single-pass processing

- easier to ensure that flags are consistent

- downgrades some diagnostics about nonconformant code from errors to
  warnings. Oddly enough, the errors actually arise from STL library
  elements shipped with gcc itself. Affects kahip compilation with
  gcc-6, gcc-7

- primary points for an external user are the polyMesh constructor

- add config info for gcc-7.3.0

COMP: intel-2017. Ignore unknown pragmas. Disambiguate method resolution.

- sentinel was not working properly when building user-space routines

- required if there is no system openmp and libomp or libgomp are
  only found in the clang hierarchy

STYLE: add some notes in the openmp rules.

- the _OPENMP macro is now used in low-level testing files

- allows enabling new warnings without causing messy output with older
  clang versions

- initial settings for ADIOS2, linuxARM64Gcc, linuxARM64Clang

- unknown options or missing option values now emit a shorter message
  without the entire usage. This makes it easier to identify the errors
  and is better aligned with the behaviour of GNU system tools.

  ====
     $ simpleFoam -case
     Using: OpenFOAM-plus (see www.OpenFOAM.com)
     Build: plus-01234

     Error: option '-case' requires an argument

     See 'simpleFoam -help' for usage
  ====

- provide for reduced (-help) and full (-help-full) usage information.
  In many cases the reduced usage provided sufficient and easier
  to find the information.

- make -srcDoc an alias for -doc-source

- no warnings about option aliases for future dates.

- add -compiler=NAME option to remove a build or platforms directory
  corresponding to any specified compiler on the current arch.

- when -compiler or -compiler=NAME is specified, also clean related
  sub-directories as well. This will cleanup mpi-related directory.

- the USE_OMP preprocessor symbol is also defined with the openmp
  compile flag to allow conditional compilation of openmp-specific
  code.

- improve functional compatibility with DynList (remove methods)
  * eg, remove an element from any position in a DynamicList
  * reduce the number of template parameters
  * remove/subset regions of DynamicList

- propagate Swap template specializations for lists, hashtables

- move construct/assignment to various containers.

- add find/found methods for FixedList and UList for a more succinct
  (and clearer?) usage than the equivalent global findIndex() function.

- simplify List_FOR_ALL loops

- the cray C/C++ compilers appear to be option-compatible with gcc.

- no wmake rules for 32bit builds (deemed to be unnecessary)

- not yet release, but some of the API and file locations are closer
  to 1706 than to 1612. Needed, for example, for swak4foam.