Parse python sources for stdlib list all the way back to 2.3

[thatch]

For comparisons against other choices, see

• https://gist.github.com/thatch/1c7139c9946a4e7d6cd65735f000c48e (vs stdlib-list)
• https://gist.github.com/thatch/ebd7e1e94b13104753ba0f5e6455cc12 (vs isort 2.7)
• https://gist.github.com/thatch/f624dac8b4c63cebbc89836dd5d14574 (vs isort 3.9; yes sre removal is real)

[amyreese]

Also, it looks like the generated py* modules aren't included?

[thatch]

I still think we should resolve the offline discussion about these being "modules" -- "top-level names" is technically correct, but both wordy and I don't think most people would understand unless they're involved in packaging.

Here's the current diff vs 3.10 (stdlibs.old is prior to this PR; I don't have a copy of 3.10 handy on this machine).

>>> stdlibs.old.module_names  - stdlibs.py310.module_names
frozenset()
>>> stdlibs.py310.module_names - stdlibs.old.module_names
frozenset({'_ctypes_test', 'xxsubtype', '_testmultiphase_nonascii_latin', '_testbuffer', '_scproxy', 'xx', '_xxsubinterpreters', '__phello__', '_overlapped', '_testimportmultiple', '_testmultiphase', 'xxlimited_35', '_testconsole', '_xxtestfuzz', '_testcapi', '_testinternalcapi', 'xxlimited'})

The names _ctypes_test, _testcapi and __phello__ are importable on my Arch install of 3.8. If they're not considered "stdlib" I'm very confused.

[amyreese]

Docs need updating, and fetch needs a copyright header, but otherwise I'm 👍 on this. If you want to squash or whatever, go for it and let me know when you're ready for a merge.