- 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

- Any trailing whitespace when parsing from strings or character buffers
  is ignored rather than being treated as an error. This is consistent
  with behaviour when reading from an Istream and with leading whitespace
  being ignored in the underlying atof/atod, strtof/strtod... functions.

- Allow parsing directly from a std::string instead of just from a 'char*'.
  This reflects the C++11 addition of std::stod to complement the C
  functions strtod. This also makes it easier to parse string directly
  without using an IStringStream.

- Two-parameter parsing methods return success/failure.
  Eg,

      if (readInt32(str, &int32Val)) ...

- One-parameter parsing methods return the value on success or
  emit a FatalIOError.
  Eg,

      const char* buf;
      int32Val = readInt32(buf, &);

- Improved consistency when parsing unsigned ints.
  Use strtoimax and strtoumax throughout.

- Rename readDoubleScalar -> readDouble, readFloatScalar -> readFloat.
  Using the primitive name directly instead of the Foam typedef for
  better consistency with readInt32 etc.

- Clean/improve parseNasScalar.
  Handle normal numbers directly, reduce some operations.

- consolidate word::validated() into word::validate() and also allow
  as short form for string::validate<word>(). Also less confusing than
  having similarly named methods that essentially do the same thing.

- more consistent const access when iterating over strings

- add valid(char) for keyType and wordRe

- use allocator class to wrap the stream pointers instead of passing
  them into ISstream, OSstream and using a dynamic cast to delete
  then. This is especially important if we will have a bidirectional
  stream (can't delete twice!).

STYLE:

- file stream constructors with std::string (C++11)

- for rewind, explicit about in|out direction. This is not currently
  important, but avoids surprises with any future bidirectional access.

- combined string streams in StringStream.H header.
  Similar to <sstream> include that has both input and output string
  streams.

- STLpoint.H
- isoAdvection.C
- checkMesh/writeFields.C

STYLE: drop construct STLpoint(Istream&), since it doesn't make much sense

- No use case for reading via an OpenFOAM stream and tokenizer.
  Should always be parsing ASCII or reading binary directly.

- elminate the foamVtkFormatter operator() in favour of xmlAttr.
  Improves readability and the purpose is clearer.

- By definition, binary STL uses float (not double) when reading.
  The ascii STL should be the same. This reduces memory overhead when
  loading files. The older triSurface reader had float, the surfMesh
  reader had double, but now has float.

- Inconsistency in the STL merge-tolerances between triSurface reader,
  surfMesh reader and WM_SP vs WM_DP. Now use consistent tolerances
  conrresponding to 10,100 * doubleSMALL.

- Similar float/double code adjustments for TRI format since this is
  very similar to the STL reader and had a similar inconsistency between
  the triSurface and surfMesh version. The AC3D reader still uses
  double when reading, but this can be revisited in the future (and can
  then remove the stichTriangles method too).

- with the xml append format it is possible to write raw binary
  (instead of base64), but the writer becomes more complicated.
  Either needs two passes to create, or need to allocate a block
  of space for the header information (like VTK itself does) and
  write later.

    * internalWriter
    * patchWriter
    * surfaceMeshWriter
    * lagrangianWriter

 Also these special purpose ones:
    * foamVtkWriteSurfFields

- this shifts responsibility away from caller to the individual writers
  for knowing which file formats are supported and which file ending is
  appropriate. When the writer receives the output format request,
  it can elect to downgrade or otherwise adjust it to what it can
  actually manage (eg, legacy vs xml vs xml-append).

  But currently still just with legacy format backends.

- relocated to dedicated foamVtkOutput namespace. Make it easier to
  obtain a formatter directly without a foamVtkOutput::outputOptions.
  Make the logic clear within outputOptions (avoid previous, cryptic
  bit masking). foamVtkOutput::legacy also becomes a namespace instead
  of a class. Relocate commonly used things into src/fileFormats, leave
  volField-related parts in src/conversion.

- can avoid allocating/reallocating SubList

STYLE: don't need NamedEnum for ensightCells, ensightFaces lookup

- now explicitly check for "SOLID" or "solid" in the header

- does not affect triSurface in the master branch, since that used a
  different parser.

Resolves bug-report https://bugs.openfoam.org/view.php?id=2455

- initial step in reducing duplicate IO for triSurface.

- write STL triangle using common core routines from fileFormats

Enhancements

- introduce intermediate layer for base64 foamVtk formatting
- add encodedLength() method, which is useful for xml appended output

- provide headerType typedef in foamVtkFormatter, foamVtkOutput

- remove byteOrder and headerType constants from foamVtkFormatter
  since the same strings can also be obtained from foamVtkPTraits

- additional convenience methods in foamVtkFormatter

- was erroneously using global sizing for offsets instead the processor
  local sizing.

--

STYLE: adjust variable naming, indentation for consistency

- remove remnant nullptr check

Resolves bug-report http://bugs.openfoam.org/view.php?id=2356

- increases coverage.

STYLE: relocate some core pieces into fileFormats

Note: classes are prefixed with 'foamVtk' instead of 'vtk' to avoid potential
conflicts with VTK itself.

foamVtkCore
~~~~~~~~~~~
- General very low-level functionality.

foamVtkPTraits
~~~~~~~~~~~~~~
- Traits type of functionality for VTK

foamVtkOutputOptions
~~~~~~~~~~~~~~~~~~~~
- The various format output options as a class that can be passed to
  formatters etc.

foamVtkCells
~~~~~~~~~~~~
- Intended for unifying vtkTopo and PV-Reader code in the future.
- Handles polyhedron decompose internally etc

foamVtkOutput, foamVtkFormatter
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Output helpers.
- Selector for individual formatters.
  Currently write all scalar data a 'float' (not 'double'). Can
  revisit this in the future.