Enable injection of custom TCP/SSL socket classes.

Twitter::Streaming::Client class now accepts custom TCP/SSL socket
classes. It passes those along to Twitter::Streaming::Connection.

It's possible to inject custom sockets this way, which in turn
makes it easy to use Twitter::Streaming funcitonality with
Celluloid::IO.

Celluloid's Socket classes support both blocking and non-blocking
operations.

https://github.com/celluloid/celluloid-io/wiki/Using-Celluloid::IO-with-existing-Ruby-libraries
Proper rspec matchers used in specs.
RuboCop's suggestions implemented.
Merge branch 'injectable_connection_sockets'

Conflicts:
	lib/twitter/streaming/connection.rb
	spec/twitter/streaming/connection_spec.rb