Initial work on the precedence parser for binary exprs.
Initial work on the precedence parser for binary exprs.

This change adds a simple precedence parser to
recognize binary expressions.

Signed-off-by: Roberto Raggi <5b38c5be65ca2d75b92c40e91029e90f276fd4fe@gmail.com>

robertoraggi/cplusplus,robertoraggi/cplusplus,robertoraggi/cplusplus,robertoraggi/cplusplus,robertoraggi/cplusplus,robertoraggi/cplusplus