Ogg: Introduce new functions ogg_sync_fseek(), ogg_ftell(), ogg_next_page(),
ogg_stream_next_page(), ogg_sync_last_page_before(), and
ogg_stream_unpack_page(). Use ogg_sync_* for ogg_read_first_page(). Bump libogg
version requirement from 1.1.3 to 1.3.0 as LibOgg 1.3.0 is required for
ogg_stream_pageout_fill() and ogg_stream_flush_fill().
Opus: Add opus support. Document added commands
SFC_(GET|SET)_ORIGINAL_SAMPLERATE. Added or extended tests ogg_opus_test,
compression_size_test, floating_point_test, lossy_comp_test, string_test,
external_libs_test. Change Opus to non-experimental.
