Initial constructor with image loading
Add an appendTo() method
Merge branch 'image-loading' into develop
Add mousedown event

I also had to switch to straight up asynchronous testing since we have to
wait for the images to load up before initializing the knob.

There's one failing test, but I can't figure out why. Logging the value
shows that it's correct, but the expectations are wrong. Ignoring it for
now since it doesn't seem to have any actual consequences.
MouseUp event
Merge branch 'mouse-events' into develop
basic rotate + some helpers
Fix percentToAngle helper
Finish up rotation
Remove unnecessary comments
Merge branch 'rotation' into develop
Remove erase() from public api
Make example knob a bit smaller
Add custom rotate event