Remove rails dependency

[Neodelf]

Guys, now the gem has rails dependency. It helps with developing some general features. But if we remove it, we will be able to work with all Rack-oriented applications. So here we can discuss that removing process. Please feel free to ask any questions!

[pineapplethief]

I guess we could use sinatra instead and mount it a-la sidekiq. I would suggest using sinatra as a peer dependency to give client apps more flexibility and avoid version resolution conflicts. We also would need to figure lowest common denominator, i.e. minimum requirements on sinatra version in order to work. I think reading sidekiq source code would be useful for that.

[Neodelf]

Nice suggestion. But I read code of sidekiq and figured out that it doesn't have sinatra dependency. They wrote code that uses only rack.