Avoid check for defined?
Revert "Implement parallel map using Celluloid::Futures"

This reverts commit fab85db8c5c284937c396e1bff77dddc64dfe0c0.
Implement Twitter::Streaming::Client
Add on_request callback
Implement additional Twitter::Streaming::Client methods
Remove Celluloid dependency from Twitter::Streaming::Client
Replace Twitter::Streaming::Request with HTTP::Request