[bugfix] #2 #3 - Fixed Constraints::notBlank() and Constraints::isBlank()
- Updated Constraints::notBlank() to properly validate against 0, '0', and null.
- Updated Constraints::isBlank() to properly validate against '' and null.
Merge pull request #6 from Myzaree/master

Fixed issue #2 Constraints::notBlank() and issue #3 Constraints::isBlank()