Enable codecov checks for project + patch
Enable codecov checks for project + patch

This will allow codecov to post checks indicating whether the code
coverage after a PR is still acceptable.

The checks try to enforce coverage is at least preserved in the code
("auto"), with a threshold of up to 1% drop still being acceptable.

igrigorik/vimgolf,igrigorik/vimgolf,igrigorik/vimgolf,igrigorik/vimgolf