Parse normal list-forms, including GSPEC, but fail to print them

Parsing of lets (even with ;'s) works; absyn post-processing doesn't

src/parse compiles but parser broken.

Completed change to remove LISTRULE form from grammar. Instead, all
list syntax is handled with embedded ListForms within normal rules.

Write a function to find possible "list" reductions within a phrase

Will need lots of test-cases as it's painfully complicated

WIP for change to list syntax handling.

Very broken at the moment