Some API deprecation -- ExperimentalAgc and ExperimentalNs are gone.
We're continuing to carry iSAC even though it's gone upstream, but maybe
we'll want to drop that soon.
Since we cannot rely on the API to be stable upstream, let's start
making the pkg-config, library, and include dir have a version suffix.
This will allow different downstream projects depending on us to
independently switch versions without packagers having to jump through
hoops.
