Features and regression fixes

• validate with Python 3.12 (#313)
• drop support for Python 3.10 (#313)
• move build configuration to pyproject.toml (#316 #317)
• evaluate constant to a Python literal when possible (#304 #320)
• fix comments_re and eol_comments_re so they effectively can be None (#307 #312 #314)
• skip over whitespace and comments before memoizing (#305 #306 #309 #318)
• verify that () parses to None or is ignored (#308)