<float.h> is now implemented in the platform independent portion. It is based

upon a macro family defined in _PDCLIB_float.h, which is similar in structore
to the existing _PDCLIB_int.h. It is controlled by three definitions in
_PDCLIB_config.h, which define which IEEE 754 format the floating point types
are in. This removes a GCC dependency from all of the targets, and should help
in making PDCLib support other compilers