This ensures the file displays correctly on GitHub. This also fixes a
few minor typos and the format of the Vim modeline, which wasn't being
detected previously.
The most "important" change here is to remove the checkboxes for
"Tests Written" on the pull request template. Because they're checkboxes
rather than radio buttons, no matter which one you checked it would show
"1/2 complete" for any references to that PR in other issues.
