Rewrite symbols.py

[pfalcon]

The original code didn't have enough power to handle modern Python, and was patched by me in more or less adhoc way. And test_super.py still excluded from testing, because handling it requires truly crazy patchings.

Instead, consider rewriting it. Like, from scratch of close. While doing that, consider being compatible with https://docs.python.org/3/library/symtable.html