include r_binary_op later so that it knows about Na_Proxy
simplify Comparator, moved the NA logic to the lower level dispatched by comp_op_type
simplify logical binary comparisons between Vectors and primitives. Using logic from comp_op_type. Moving Comparator_With_One_Value inside Comparator.h
no longer needing sugar::less, sugar::greater, ... generated by RCPP_OP macro