Allow releasing 2.0.x branch

[ghostdogpr]

I'd like to do a 2.0.x release with the performance improvements that have been pushed to that branch. I think that change is all we need to do that.

Independent question: what's the plan for 2.1? Are there more things to be included? Are the runtime changes complete/stable?

[jdegoes]

@ghostdogpr Mostly it just needs to be merged with master and we need to do one RC for 2.1. There's nothing else that needs to be in there, even though there is some followup work I will do in May.

[ghostdogpr]

Ah your 2.1 changes are already in the "main" branch (series/2.x), which is why I backported some improvements to series/2.0.x so we could release them.

@kyri-petrou and I are currently looking at the ForkJoin improvements, so I'll wait a bit to see if we find anything and then do a 2.1.0-RC2 (there was a RC1 in December).