Add support for 10/11/16-bit floating-point values.

These are referred to (in this code) as "small-floating-point" numbers.

Supporting these requires special code, as C++ doesn't support these types.
The GL_HALF_FLOAT "type" corresponds to 16-bit floating-point values, where the
OpenGL semantics and IEEE semantics seem to be the same.

The 10-bit and 11-bit floating-point values seem to be only for OpenGL, and
have special semantics (e.g. are only positive values), and are only used for
one format-type combination (i.e. GL_RGB/GL_UNSIGNED_INT_10F_11F_11F_REV).

Support includes handling INFINITY and NaN (i.e. "not a number").
Added support for GL_BGR[_INTEGER] combos.
Address feedback/requests from Rich.

Including the following:

- Added function (2 versions) to query info about an fmt.

- Add rtn value and size parameters to pxfmt_convert_pixels().

- Add alt_*_row_stride param's to pxfmt_convert_pixels().

- This includes minor changes to ktxtool to reflect the changes to
  pxfmt_convert_pixels().
Merge pull request #64 from IanAtLunarG/pxfmt_140513

Pxfmt 140513