[Feature][ActiveRecord::Enum] adds method for getting enum label from integer

[Anthony Hernandez]

I'd like to open a PR for this -- I have the change written and ready to go. It's simple enough. The idea is to provide a "nice" way for going from an integer returned from the database

to the corresponding label defined for an enum field without resorting to hash methods. I've written up details (and the change) here:

https://github.com/rails/rails/commit/379c899479e31b47956fa667ec656a185034e910