rename local fn `eat` to `adv` in type expr parser
uncommented older parser tests, added `val ... =`

No top-level parser function for parsing exprs, only decls
added singleton type var bindings in datatype declarations
added multiple type var bindings in datatype declarations
added todo
updated todo
added Makefile for parser and parser tests as standalone
deleted grammar comment, need to update it and carefully confirm correctness
parser code for literal tuple expressions
parser code for tuples in patterns