Added support for < and > operators. This isn't very *important* but does make expression composition of constraints a lot nicer to use.
Neatened up a lot of code, including removing some apparently dead code (which was in the public interface, and thus requires a major version bump)

Signed-off-by: Martin Evans <martindevans@gmail.com>
bumped version for recent changes (major bump)

Signed-off-by: Martin Evans <martindevans@gmail.com>