[opus] First Version of OpusDrop

[Timothy B. Terriberry]

Martyn Shaw wrote:
> I would like to see OPUS supported in Audacity (and I'm an Audacity
> developer) but I don't have the time to do it.  Does anybody else?  I
> would be willing to support this in term of getting it tested and
> committed.  We already support OGG and Vorbis, Monty used to be on the
> team here.  But I don't know much about the libraries.

Audacity uses libvorbisfile, so adapting that code to use libopusfile 
[1,2] for Opus should be pretty straightforward.

[1] http://git.xiph.org/?p=opusfile.git
[2] 
https://mf4.xiph.org/jenkins/job/opusfile-autotools/ws/doc/html/index.html