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 non-blocking sockets this way, which in turn
makes it possible to use Twitter::Streaming funcitonality with
Celluloid. The Connection class blocks the Actor's mailbox otherwise.
Merge branch 'injectable_connection_sockets'

Conflicts:
	lib/twitter/streaming/connection.rb
	spec/twitter/streaming/connection_spec.rb
Changed names of *_socket_klass to *_socket_class.