~mna/snow unlisted

snow/doc d---------
pkg/{parser,semantic,codegen}: more test cases
Merge branch 'wip-generics'
pkg/semantic: more work on types for generics
doc: think about gens
doc: think some more about generics
cleanup some todo comments
Merge branch 'wip-tuple'
pkg/codegen: fix missing go nodes in position assignment
pkg/typecheck: refactor scope type to add depth, more flexibility
pkg: much progress on name mangling
pkg/codegen: work on name mangling
pkg/{parser,token,scanner}: add name mangling rune, Go keywords
doc: add python and swift grammars
doc: add Go EBNF grammar for easy reference
pkg/typecheck: add tests for nested func, assign to let
document typechecker choice cuts from go
doc: document compiler stages