MSVS does defined the M_LN2 constant in <math.h> but only makes it
visible if _USE_MATH_DEFINES is defined.

Patch-from: lvqcl <lvqcl.mail@gmail.com>

finished integerized flavor of library; sections with floating point are either #ifdef'd out or written in fixed-point

first pass at making an integer-only flavor of the libraries.  move FLAC__real out of ordinals.h to src/libFLAC/include/private/float.h, add FLAC__double and FLAC__float and use these everywhere instead of double and float, and don't typedef FLAC__real/float/double when building in integer-only mode.  still need to provide integer substitutes in several places.