Option for sharp grid lines, and a few minor things

G'day Joe!

Due to the canvas's sup-pixel rendering, grid lines were appearing blurred across physical pixels. I've added a boolean option that allows them to be sharp. The default is unchanged. There's also a new example that allows runtime manipulation of this feature in order to see the difference.

There are a few minor fixes as well such as semicolons and typos. These are all in different commits in case you want to cherry pick the bits you like, if any.

I've started using smoothie charts recently in a telemetry dashboard I'm building for our humanoid robots, to show things such as processing times and gyro/accelerometer output. The library is fantastic, so thanks very much. These thinner lines made my charts a bit easier to read as I'm dealing with rapid data values (over websockets) and thin series lines.

Drew.