[opus] Opus main branch

[Jean-Marc Valin]

Hi everyone,

Despite the mailing list being relatively quiet recently, there have 
been a lot of improvements and new features added to the Opus code. 
Those have all been in the opus-ng side branch and are now ready for 
wider use. While doing that, the plan is also to follow the new 
convention and change the default branch name to "main" instead of "master".

So unless there's any issue, some time in the next few days, we will:
1) Rename "opus-ng" to "main"
2) Make the new "main" branch the default branch
3) Delete the "master" branch

In the mean time, if you do see issues with the opus-ng branch, please 
let us know, so we can address them.

Cheers,

	Jean-Marc