Add ability to load env-t settings from each *.env file.

I think it would be a good idea to autoload settings from any *.env file in Rails app in addition to '.env' or ".env.#{Rails.env}". 

With this little patch we can create files: 
- "config/environments/constants.env" (All non-secret constants) 
- "tokens.env" (file with secrets).

This would be helpful for capistrano deployment:
    
    set :linked_files, %w{config/database.yml config/environments/tokens.env}

We can link only tokens.env, without constants.env. 

In addition I think 'semantic_name.env' would be more semantic than just '.env'.

Thanks in advance for your attention!

UPDATE: All previous '.env' and '.env.*' conventions will work as before.