Doesn't support 'retina' screens

I'm not well versed enough in canvas to do a pull request for this. http://www.html5rocks.com/en/tutorials/canvas/hidpi/ explains things quite well though.

[9mm]

I second this, although I'm not sure how hard it is to add. Looks really blurry on my screen.

[toabi]

I'd also like to have retina/hidpi support for this project.

[brianr]

+1. Any chance #121 will get merged?

[jdelman]

I'd also like to see #121 get merged.

[rept]

Same here.

[stringfellow]

👍