refactor Channel::channelClose to just Channel::close
split channel tests into their own executable

Refactored tests specific to QAMQP::Channel into its own full test
case, as there are more on the way
add test for sharing a channel

Though it's not necessarily recommended (per spec), Channels can be
shared by multiple Exchanges and Queues. I've added a test here showing
that's possible with QAMQP