Allow arbitrary python version

[spinus]

Currently pypi2nix has fixed set of python versions. Would really like to have -V to set arbitrary version, even if it's not in pypi2nix yet (but is in nixpkgs). That could be actually "stupid" and just replace the string without any autodetection whether that version is supported in nixpkgs or not.

[garbas]

@spinus 👍 yeah we should loosen this. care to provide a PR for this?

[seppeljordan]

Since this will mean a lot more maintenance work supporting peoples weird ideas this is a "Won't implement" at the time. This might change with more contributers.

[spinus]

@seppeljordan I know it's closed but anyway. What about adding a switch --I-promise-to-not-open-a-ticket-and-bother-people-I-just-want-to-try-to-use-another-python-version-as-an-adult-person-I-want-to-take-a-risk-without-maintaning-my-fork or maybe not 100% this but in that spirit?

[seppeljordan]

would be acceptable.