Update files to match the opus-1.0.0 source release.
This corresponds to the spec implementation included
in RFC 6716.
Changes from the previous in-tree version (draft-12):
- Add extern "C" protection on opus_multistream.h.
- Align to sizeof(void*) instead of 4 bytes.
- Copyright header updates for IETF publication.
- Minor documentation and whitespace fixes.