Add support for checking channel and queue size

This feature simply aggregates the number of events in all queues, resulting in
channels might return a larger number than expected when consuming multiple queues
that contains duplicates
Add basic support for channel metadata
Fix missing pid return in meta/3
Add clause in meta/2 to get all meta attributes
Allow integers in meta/4
Add test to ensure that named queues/chans plays nicely
Use links instead of monitors for `redq_chan`
Tag 0.2.1