Cleanup FLAC__bitmath_silog2()

- Retire 32bit variant of silog2(), since only the _wide variant is used
- Rename FLAC__bitmath_silog2_wide() to FLAC__bitmath_silog2()
- Replace existing implementation by shorter, clearer implementation
  using optimised routines from bitmath.h
- Update Copyright string to 2016 in changed files

Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
Closes: https://github.com/xiph/flac/pull/6
3 files changed