New API for checking pending message count
New API for getting a specified set of messages

This will be easier to use in some cases where we have to get
only a specified set of messages. This API uses the __iter__
API internally, but maintains the state to give back only the
required set of messages

API is - get_messages(count=1)
Missed a doc string
Adding a debug statement
Closes #22

Removed get_messages API, added test for get_pending
Merge branch 'issue-22'

Conflicts:
	kafka/consumer.py