Bug due to the changes in qntm/greenery v4.0.0

[gihyukko]

Just noting that the changes in the most recent version of greenery (that is, >=4.0.0) causes bug in using ptype.
It seems greenery.lego -- which ptype seems to depend on -- no longer exists in v4 (please see qntm/greenery#67).

Steps to reproduce the bug

Run the following in an empty virtualenv with no pip packages installed.

$ pip install ptype
$ python3
Python 3.10.5 (v3.10.5:f377153967, Jun  6 2022, 12:36:10) [Clang 13.0.0 (clang-1300.0.29.30)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from ptype.Ptype import Ptype
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/site-packages/ptype/Ptype.py", line 10, in <module>
    from ptype.Machine import PI
  File "/Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/site-packages/ptype/Machine.py", line 3, in <module>
    from greenery.lego import parse
ModuleNotFoundError: No module named 'greenery.lego'

Also noting that testing with greenery==3.3.7 worked fine.

Thanks!