func_adl v2.1

One big user-facing change:

• It is now possible to use lambdas directly in calls to Select, SelectMany, and Where. Heuristics are used to recover the source - so it won't be perfect. But should work for most use cases. So much nicer!

And one under-the-hood change. This package is now compatible with python 3.8 and 3.9. However, several packages above this need to have the same treatment done, and then cross-checks to make sure that a 3.8 or 3.9 client can send to a 3.7 backend must occur. But this is a first step!