Use zerogc for allocation

[Techcable]

This will allow python code to access the generated AST, hopefully obseleting the CPython 'ast' module. Note that I've made a few changes from the CPython AST that would complicate this integration (we would have to add some sort of wrapper objects).

It will also allow the parser and bytecode compiler to use garbage collected collections like hashmaps, which would otherwise need to be allocated with malloc.

Hopefully this will also reduce memory usage of the parser and maybe even increase speed.