fix bug in parsing of patterns, allow patterns to be parenthesized
updated todo
fix test
added type inference code for tuples
experimentally treat Ctor in atexp as Id

n.b. this might end up being a disasteradded type inference code for tuples
parser continues after a single decl, returns a list of decls (i.e. 'a Program.t)
(wip) change 'a Decl.t to ('a, 'b) Decl.t
added module Constraint for type constraints
rename TypeInf.info to TypeInfo.typed
allow Env module to be used elsewhere in TypeInf, use StringMap
rename typeinf to typecheck
move Parser.SyntaxError into public sig
Typecheck.assignTypeVars takes an env (gamma)
(wip)
(wip)
added AST.walk utility functions