Added the option to load .env from an url with the same cmdline paramete...

Hi, I've started this branch to experiment with an idea that I've been using here. I think that the possibility to load the .env file from an internal webserver or a dynamic application is good to deploys that come straight from my git server. 

I've added the option to pass an url to --env when starting foreman and it worked well for me. I don't know if this is desirable or if it breaches any of concept of foreman or 12factors (it didn't seem to when I looked it up).

I've made a toy example of an automatic env file generator https://github.com/gleicon/config_server. The idea is to emulate what heroku config:add. 

If this sounds like a good idea and you have any guideline that you think I should followed please let me know, I'd be happy to dig in. 

Thanks a lot for the great work.