update expected error messages to be unification errors, when they are equivalent to previous non-unification errors
fix handling of record types in unification - both width subtyping and handling the error condition properly
fix bugs in ct-to-ty, add monadic option functions, delete some dead (and commented out) code
fix bug: named types introduced by data weren't getting picked up (how this wasn't causing more errors before... I have no idea)
bind type parameters when type checking constructors, so the type T is not undefined
cleanup: deleting tysolve, the unification over types, moving around code, adding comments, adding README todos