ability-to-load-envs-from-config-path

As we discuss in the pull request ([dotenv#102](https://github.com/bkeepers/dotenv/pull/102)) I am submitting a patch, which allows to store *.env files in `#{Rails.root}/config` path.
All *.env files in the config path will be autoloaded for Rails apps.
All the previous '.env' and '.env.*' conventions will work as before.

##### Examples:
- "config/environments/constants.env"
- "config/api_keys.env"
- "config/whatever.env.production"