Continuously reconnect when recovering from network failures

Fixes #25
Bring back HotBunnies::ThreadPools

We still let people override per-connection executor.

Conflicts:
	lib/hot_bunnies/thread_pools.rb
Merge branch 'master' of github.com:ruby-amqp/hot_bunnies

Conflicts:
	lib/hot_bunnies/session.rb
	lib/hot_bunnies/thread_pools.rb