Merge pull request #107 from jacksonh/prAssignee

Add assignees to pull requests.
Merge pull request #105 from jacksonh/pullSync

Add the syncronize action for pull request events
Add path, position, and body properties to pull request comments.
Correct implementation and comments for position / originalPosition
Add the commitSHA property to pull request comments.
Add original_commit_id, clarify docs, add more tests.