[keepalive] specify custom keepalive check attributes in client data
[keepalive] set check name, issued, and executed after merge
[keepalive] deep merge check & client keepalive config
[prefetch] allow users to set rabbitmq prefetch (channel)
           - consumers w/ no_ack ignore prefetch (client queues etc)
Merge pull request #633 from portertech/keepalive

Specify custom keepalive check attributes in client data
Merge pull request #634 from portertech/prefetch

[prefetch] allow users to set rabbitmq prefetch (channel)