Added documentation for the EqualConstraint
Added docs for NotEqualTo validator
Added docs for IdenticalTo validator
Added docs for NotIdenticalTo validator
Added docs for LessThan validator
Added docs for LessThanOrEqual validator
Added docs for GreaterThan validator
Added docs for GreaterThanOrEqual validator
Merge pull request #2599 from WouterJ/document_equal_validators

Documented the Comparison validators