Coverage remained the same at 100.0% when pulling 36a7dda on mondwan:master into d7f6baa on ansman:master.

refs #99
As consensus of what should be defined as isDefined are hard, I have introduce excludes for adding custom exclusion logic on top of 3 validators: format, inclusion and numericality. (For proof of concept and suite my production requirement)

It does not break existing implementation (isDefined) but allows users to exclude certain value before running a desired validator

Currently, excludes requires an array of function or constraint (I name them as hooks) and will be passed to shouldValueBeExcluded for verification. It will skip the validator if either hook return true.