Adding get_current_context() method
Add MessageIterator for pulling work off a pull queue.

Add a MessageIterator which pulls messages off a specified pull queue in
specified batch amounts. It exposes an iterator to go over the messages and
send out the payload from the messages
removing further reference to _executing_async in get_current_context
Remove get_messages call as the MessageIterator does what's needed.

get_messages is no longer needed.
Fixed typos in the comments and the Exception. Also fixed if condition to check registry
Merge pull request #25 from beaulyddon-wf/message_iterator

Add MessageIterator for pulling work off a pull queue.
Merge pull request #24 from tannermiller-wf/get_current_context

Adding get_current_context() method
Merge branch 'master' of wfgithub:WebFilings/furious into persistence-api