Move some of backend to LSTS syntax

[andrew-johnson-4]

LSTS syntax is a lot nicer to read and maintain.

[andrew-johnson-4]

LSTS frontend TODO:

✓ replace String with SmartString in types ✓ replace CString with String in types ✓ parse ascription :: in expression position ✓ parse match expression ✓ parse string destructuring on LHS ✓ parse String literals ✓ parse regular expressions (just punt to regex.h for now) ✓ parse format strings in string literals ✓ parse complex types with <> [] , compounds ✓ parse let bindings ✓ parse comments

[andrew-johnson-4]

PRIORITY ports from LM to LSTS

• type system
  • derived types with corollaries
  • derive Fields with fast-forward propositions
  • 100% error message coverage with good errors
  • add support for distinct arity per type Tuple<x,y> vs Tuple<x,y,z>
  • add support for multipass inference with Algorithm W
  • add support for corollary functions and guided inference