Populate kanin module with multi-arity API functions

[oubiwann]

There need to be n-1 and n arity function calls for every channel-related call:

• n-1 for all calls that will use the default channel
• n for all calls that will provide for explicitly naming the channel to use

This task will be updated with the full list of functions that need to be implemented once task #9 has been completed.

Note that all of the functions will call into the supervised kanin gen server (which in turn makes the Erlang client lib calls).

Part of feature #8

[oubiwann]

Only a few functions from the low-level API have been wrapped; just those needed for now. If users want others to be included, we can easily do so.