Fix bin_op2 -> bin_op1 in tree grammar (#61)
Minor AST rewrite changes to tiger.g->numExpr3, alt 3 + tree grammar work
Ref issue #61, #63
Add some action rules for numExpr1 .. 3 (#61, #63)
Add some parser actions for boolExpr1 .. 2 (#61, #63)
Extra minor changes in tigerTreeWalker.g (#61)