Fixups for minProperties, maxProperties, minLength, maxLength
Fixups for minProperties, maxProperties, minLength, maxLength

Previously the parser would error unless the values were positive integers, although the spec allows them to be zero.  This is now fixed.

Also fixes up a few incorrect KWS_* constants.

katef/jvst,sfstewman/jvst,sfstewman/jvst,katef/jvst