Updated github.js to include better issue api coverge.
Various tweaks as well.

-- github.js --
Github.Issue.assignees
Github.Issue.event
Github.Issue.repoEvents
Github.Issue.issueEvents
Github.Issue.comment
Github.Issue.repoComments
Github.Issue.issueComments
Github.Issue.label
Github.Issue.labels
Github.Issue.issueLabels
Github.Issue.milestoneLabels
Github.Issue.milestone
Github.Issue.milestones