Github: unfold commit history

Adds "unfold all changesets" buttons (hotkey: f) above/below Commit History pages at github, letting you browse the source changes without leaving the page. (Click a commit header again to re-fold it.) You can also fold or unfold individual commits by clicking on non-link parts of the commit. As a bonus, all named commits get their tag/branch names annotated in little bubbles on the right.