Add QueueingRabbit::Client::Bunny#next_tick and QueueingRabbit::Client::AMQP#next_tick methods to be used for POSIX signal handling.
Use #next_tick for all POSIX signals processing to properly shut down workers on Ruby 2+.
Add new #purge_queue method for all connection adapters.
Bump version number.
Add Ruby 2.1.0 to .travis.yml.