Add exception based error recovery, using a list of tokens at which to recover

The following program:
(+ val x = (+ val x = = =  in foo == dah +)
   val y = mod
   val z = 42; mod; 112; mod
   in tup kat +)

Now yields the following output:
Parse error: Unexpected token
(+ val x = (+ val x = = =  in foo == dah +)
                      ^
Parse error: Expected "+)" at
(+ val x = (+ val x = = =  in foo == dah +)
                                  ^
Parse error: Unexpected token
   val y = mod
           ^~~
Parse error: Unexpected token
   val z = 42; mod; 112; mod
	       ^~~
Parse error: Unexpected token
   val z = 42; mod; 112; mod
                         ^~~
Parse error: Expected "(" at
   in tup kat +)
          ^~~
Instead of just the first error