Update version to 2.1
Update version to 2.1

I think we will likely call release 3 “v2.1” since that reflects the
magnitude of the change.

bbc/ebu-tt-live-toolkit,ebu/ebu-tt-live-toolkit,ebu/ebu-tt-live-toolkit,bbc/ebu-tt-live-toolkit,bbc/ebu-tt-live-toolkit,ebu/ebu-tt-live-toolkit