Allow the symmetric and asymmetric keywords to the between predicate

When testing whether a number c3 is between c1 and c2, sometimes you don't know when c1 <= c2. In this case it is useful to be able to run "c3 between symmetric c1 and c2" which handles the case of c1 > c2. SQL allows the keywords of symmetric and asymmetric to be defined, with asymmetric used if no keyword is supplied. SQL standard reference: section 8.3