Clean and understandable model for recurring re-encryptions

[DmitryDrobotov]

Will be great to have special class/self-method which takes settings from somewhere (e.g. transcryptor.yml) and re-encrypts keys based on its data.

[GildedHonour]

I think there should be a config file anyway as Alex Fortuna has proposed. And there might be environment variables which will be used some variables aren't specified in the config file or the config doesn't exist.