Within decomposeParDict, it is now possible to specify a different
  decomposition method, methods coefficients or number of subdomains
  for each region individually.

  The top-level numberOfSubdomains remains mandatory, since this
  specifies the number of domains for the entire simulation.
  The individual regions may use the same number or fewer domains.

  Any optional method coefficients can be specified in a general
  "coeffs" entry or a method-specific one, eg "metisCoeffs".

  For multiLevel, only the method-specific "multiLevelCoeffs" dictionary
  is used, and is also mandatory.

----

ENH: shortcut specification for multiLevel.

  In addition to the longer dictionary form, it is also possible to
  use a shorter notation for multiLevel decomposition when the same
  decomposition method applies to each level.

- only warn about missing cells/points if the mesh is also missing
  boundary patches.
- reduce verbosity when decomposing to an empty mesh
- skip face matching when either mesh has no faces

consolidate surfaceFormats for reading/writing triSurface

See merge request OpenFOAM-plus!174

preliminary improvements for externalCoupled

See merge request OpenFOAM-plus!175

- similar idea as subCycleTime but without sub-dividing the time
  interval or incrementing time itself

- waitForSlave now return a Time::stopAtControls enumeration:

    unknown:     when lockfile has no specially recognized content.
    endTime:     when lockfile contains "status=done"
    writeNow:    when lockfile contains "action=writeNow"
    nextWrite:   when lockfile contains "action=nextWrite"
    noWriteNow:  when lockfile contains "action=noWriteNow"

These values can be used by the caller to terminate the master
(OpenFOAM) as desired in response to information placed there by the
slave process.

- use a Pair<scalar> with first() / last() residuals

- expose the names of write and stopAt controls for reuse elsewhere and
  provide a stopAtControls enum for 'unknown'

- track the requested number of sub-cycles (was previously a bool)

- found() method for consistency with other classes

- operator()(name, deflt) for similarity to lookupOrDefault,
  but without a dictionary

- the readList<T>(Istream&) function was introduced to handle command
  -options with either a single or a list value, but was also used for
  the #remove dictionary directive. However, the parsing was fragile
  if the list did not start with a '('.
  Now handle command-line arg/option list directly (via ITstream)
  and #remove with special-purpose reading of a string or word list.

  This removes ambiguity and reduces potential future problems.

STYLE: use ITstream instead of IStringStream for command-line lookups

- parses directly to a tokenList without a string copy.

- 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.

- stricter and robuster than previous solution using List::readList
  since the option input can be fully tokenized prior to list
  conversion.

- split now optionally retains empty substrings.
  Added split on fixed field width.

- Foam::name() now formats directly into string buffer, which a
  removes one layer of copying and also avoids using a non-constexpr
  in the temporary.

STYLE: explicit type narrowing on zero-padded output for ensight

- not maintained and less functionality than ccmToFoam.

Feature arglist option aliases

See merge request OpenFOAM-plus!172

- in most cases already checked valid() so don't need additional check
  for setting an existing pointer

- can be used for adjusting option names between versions

- browser is spawned as a background process to avoid blocking the
  command-line

- allows (for example) splitting a user string on whitespace and
  passing this to system as a list of arguments, thus bypassing any
  implicit use of 'sh'.

- system() with optional background, for spawning processes.

- this makes them applicable to Foam::string, Foam::word etc

ENH: improvements to CStringList

- add strings() sublist variant which can be useful when handling
  command arguments separately

- add construct from SubStrings.

- eliminates previous code duplication and improves maintainability

Feature multiple stitch mesh (wp04)

See merge request OpenFOAM-plus!164

Consistency update for list typedefs

See merge request OpenFOAM-plus!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 OpenFOAM-plus!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.