- prior to sampledSurface supporting different interpolation schemes a
  workaround means was used to simulate cellPoint -> face
  interpolation, with averaging of vertex interpolation.

  We instead now use cellPoint interpolation directly for the face
  values when 'interpolate=true'.

- normally findInstance will 'bottom out' with the constant directory
  while doing its reverse time search. This mechanism however fails
  when searching for negative start values (if there are none in the
  list). Add additional logic for this so that constant will also be
  used in these situations.

Note: to have decomposePar work for all times, may need the -constant option
to trigger the proper time list.

- construct from positions

- reset positions, minEdgeLen, find grid index

ENH: add accessor for obtaining the size of a single i-j-k dimension

- eg, obtain the 'i' dimension with any of these methods:

      ijkAddr.size(vector::X)
      ijkAddr.sizes().x()
      ijkAddr.sizes()[0]

Snappy hex mesh proximity check

See merge request OpenFOAM-plus!249

- construct/assign from Zero

- add boundBox::directionBit enum which contains the same values as the
  treeBoundBox::octantBit enum, but without the attached meaning

- These are not defined in the C++ standard for cmath, so allow for
  compilation without them. Will need to provide replacements in the
  future or rework.

- new regExpCxx wrapper for C++11 regex support with drop-in
  compatibility with existing code.

- regExpPosix (was regExp), for future phase out in favour of regExpCxx.

- The regExp header will continue to be used for defining an
  appropriate typedef corresponding to the preferred implementation.

- this information is more related to processor, not OS

- relocates some logic from makefiles/general into platform-specific
  overrides

- for more clarity, make read/write of rpm and mean-diameter contingent
  on nonDimensional == true

- write finiteArea meshes and fields to standard surface output
  formats (Ensight, VTK, etc).

- less used bookkeeping/convenience methods that may be phased out
  in the future

- instead of deciding beforehand if a surface format requires a separate
  geometry file (or if a geometry file should be written if no fields were
  written) now determine afterwards if something was written.

  This improves the overall reliability (consistency) and is more
  convenient for the caller as well.