Allow caller to specify the consumer_tag
#38 - automatically set consumer_tag to a meaningful value

This has few benefits:
 - lower bandwidth (we don't pass full amq.gen-xxx string with every message, just a short x.x number)
 - seems simpler imo
 - and most importantly - consumer tags must be unique, so it's better not to allow user to hardcode a value there.
typo
Merge branch 'master' of github.com:majek/puka