Support --target-version for Python 3.10

[jamilraichouni]

Is your feature request related to a problem? Please describe.

I plan to start using Python 3.10 and wonder what I can specify as --target-version!?

Describe the solution you'd like

black --help shall list how I specify a Python 3.10 target version.

Describe alternatives you've considered

I installed Pyrhon 3.10 and the latest black version to see if black --help lists an appropriate target version.

Additional context

I looked through open issues here before I wrote the current one.

[cooperlees]

We need to support all 3.10 syntax first before being able to target this version. #2242 is tracking that.

The support lag comes from lib2to3 deprecation and no settled replacement parser for us to use moving forward. This will be a major refactor / rewrite of black when the new parser is selected. We need all the help we can get here.

[JelleZijlstra]

@cooperlees you're out of date, we support 3.10 on main now :) We should probably do a release in the next week or so.