add 'key' method for retrieving the enum value's symbol key
Updates

Fix 'add' method to properly upcase the expected constant name for the enum
value.

Add 'get_key' method to retrieve the symbol key for an enum value.

Add 'get_from_entries' method to abstract retrieving information about a enum
value based on its value. Refactor 'get_label' to use this new method.
bump to version 0.0.2
starting to fill out explanation and examples of using RailsAttrEnum
Merge branch 'dev'