opusfile version 0.1

This is the initial release of libopusfile. Like libvorbisfile for
Vorbis files, libopusfile provides a high-level API for decoding
and seeking within .opus files. It includes:

- Support for all files with at least one Opus stream (including
  multichannel files or Ogg files where Opus is muxed with
  something else).
- Full support, including seeking, for chained files.
- A simple stereo downmixing API (allowing chained files to be
  decoded with a single output format, even if the channel count
- Support for reading from a file, memory buffer, or over HTTP(S)
  (including seeking).
- Support for both random access and streaming data sources.
- Complete documentation of the public API.
- Two simple examples demonstrating the API.

The code has undergone basic testing, but as this is the first
release, there are still likely to be issues we didn't find. Please
give feedback in #opus on irc.freenode.net or at opus@xiph.org.