love.graphics.rotate supported with new matrices

I didn't get around to this until about half an hour ago, but it was really easy. I'd already been looking at rotation support with a suspicious eye ever since the font stuff, so most of the research as to what would be necessary? Already done, I just had to [pull up a bit of refresher material to copy from](https://en.wikipedia.org/wiki/Rotation_matrix).

I added the clouds_rotate demo to show this off and prove that it works. This is a straight copy of the clouds demo, except that I've altered the nekochan:render function to use the transformation stack, rotation and translation to slowly spin Nekochan around its center.

This pull request should be pretty easy to backport to the mainline lua-parser.js. It doesn't include support for rotated fonts yet, I think that belongs in a separate issue (unless you want to hold out for that, but it would be a lot harder to backport cleanly due to the churn between the weblua branch and mainline in love.font.js).