Consistency update for list typedefs

See merge request !171

- in rare cases we may wish to have command-line arguments that are
  non-mandatory. This can now be reflected in the usage output, provided
  that the argList::nonMandatoryArgs() has been used.

- added setRootCaseNonMandatoryArgs.H that applies the
  argList::nonMandatoryArgs() settings and otherwise performs largely
  as per setRootCase.H, except that the check for mandatory arguments
  is deferred to later user code.

- constructor for empty cell/face/point Zones, with contents to be
  transferred in later.

- ZoneMesh::operator(const word&) to return existing zone or a new empty one.

cellModel enumerations

See merge request !170

- this provides a better typesafe means of locating predefined cell
  models than relying on strings. The lookup is now ptr() or ref()
  directly. The lookup functions behave like on-demand singletons when
  loading "etc/cellModels".

  Functionality is now located entirely in cellModel but a forwarding
  version of cellModeller is provided for API (but not ABI) compatibility
  with older existing user code.

STYLE: use constexpr for cellMatcher constants

- warn or fatal if Pstream::init or Pstream::exit are called multiple
  times.

- additional Pstream::initNull method as failsafe to initialize MPI
  when the underlying OpenFOAM process is not running in parallel but
  the application still needs MPI.

- Pstream::exit() can now also be called without having used MPI::init(),
  which means it can be used to cleanup serial process or for
  applications that used the special purpose Pstream::initNull()
  mechanism.

mark authored 7 years ago and Mark OLESEN committed 7 years ago

- now also fixed collated output format

STYLE: use Ostream writeEntry when writing key/value entries

See merge request !168

- makes for clearer code

ENH: make writeIfDifferent part of Ostream

- occurred when variable name exceeded the 15-char alignment format
  and the name run into the previous field.

- reduces ambiguity between matching a list of strings and a single string.

Feature function object field input

See merge request !167

ENH: support change of Pstream buffer format via flag modifier

See merge request !166

Feature field average windowing

See merge request !165

- allows changing the format of the sending OPstream at an arbitrary
  point in the transmission. The information is passed through the
  buffer and the receiving IPstream changes its format accordingly.
  This allows a temporary toggling of ASCII/BINARY mid-stream.

- support when creating modules for OpenFOAM.
  Original source from Ivan Spisso (CINECA) modified by OpenCFD

- the return value signals if this method handled this particular type
  of token. This minor change allows this method to be used as a succinct
  prefilter an output token stream. It also provides better encapsulation
  of what the particular output stream handles.

  Eg,

      bool ok = os.write(tok);
      if (!ok)   // or   if (!ok && os.good())
      {
          os << tok;
      }

  instead of

      if (tok.type() == typeA || tok.type() == typeB || ...)
      {
          os.write(tok);
      }
      else
      {
          os << tok;
      }

Also updated/corrected restart behaviour

When specifying the averaging data, a new `windowType` option is
available, taking the values:

- none: no windowing
- approximate: past functionality (v1706 and earlier)
- exact: exact moving average - will store and write (for restart) all
  fields in the window

dictionary compatibility/migration methods

See merge request !162

- when dictionary keywords change between versions, the programmer
  can use these compatibility methods to help with migration.

    * csearchCompat, foundCompat, lookupEntryPtrCompat, lookupEntryCompat,
      lookupCompat, lookupOrDefaultCompat, readIfPresentCompat, ...

  They behave like their similarly named base versions, but accept an
  additional list of older keyword names augmented by a version number.
  For example,

      dict.readIfPresentCompat
      (
          "key", {{"olderName", 1612}, {"veryOld", 240}},
          myscalar
      );

   where 1612=OpenFOAM-v1612, 240=OpenFOAM-v2.4.x, etc.