Fix Graphics.drawLine(), add drawCircle(), fillCircle(), drawRect()

[badlogic]

Need to call ctx.beginPath(), otherwise subsequent calls to Graphics.drawLine() will add up in a single path. Also applied formatting to the file. Can amend if the formatting is a no-no.

The additional methods aren't super useful for pixelart games due to non-configurable anti-aliasing of the corresponding Canvas API methods. They can be useful for debugging purposes though.