Newer versions of MSVC are unhappy with the strategy of the build
environment redefining "inline" (even though they don't support the
actual keyword). Instead we define OPUS_INLINE to the right thing
in opus_defines.h.
This is the same approach we use for restrict.
Also using the same int->float conversion functions for SILK as for CELT
and changed encoder implementation default to constrained VBR just to
be safe when VBR gets more aggressive.
