Add Validator and RegexValidator classes
Rename Validator to MaterialETValidator to avoid classpath conflict

AutoCompleteTextView has its own Validator interface in 21+
Add custom validation functionality to MaterialEditText and auto complete
Update sample activity to use custom validator
Return edittext instance in addValidator for easier chaining of validators
Update documentation
Add extra validate(validator) for single instance validations
Rename to METValidator to keep it shorter
Rename validate(validator) to validateWith(validator) to be more descriptive
Rename RegexValidator to more correct RegexpValidator
Merge pull request #29 from hzsweers/master

Custom validation interface