HumanTaskAgent can now accept `combination_mode` and `poll_options` which are used to generate a poll from the HITs answers.  The poll asks additional Mechanical Turk users to rate the responses, and then the best one is returned.  This allows for an additional step of validation on user generated content / data.
Merge branch 'master' into human_task_agent_makes_polls
doc
Merge pull request #98 from cantino/human_task_agent_makes_polls

HumanTaskAgent can now validate answers with a poll