- The 'used()' method was for transitional compatibility with the now
  defunct PackedBoolList.

  The canonical method name for returning a labelList of 'on' bits is
  toc().

- was historically defined as (1 1), but it is more consistent with
  the concept of one to have a real component only.

  Now defined as (1 0):  1+0i

STYLE: remove obscure '!' operator for complex conjugate

- either use the member function or the '~' operator

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