1.3.0

A bunch of new methods were added in #5:

• $value->getKey() Returns the key of the current value on Enum
• Enum::keys() Returns the names (keys) of all constants in the Enum class
• Enum::isValid() Check if tested value is valid on enum set
• Enum::isValidKey() Check if tested key is valid on enum set
• Enum::search() Return key for searched value

The library is now PSR-4 compliant.