Implement board render.
Implement board render.

Add property `coordScale`, mapping millimetre coordinates to pixels based on the `pixelMicrons` param.

Boards render with curves. I believe they'll deal well with slots and cutouts, as I've accidentally created one with a decal that shouldn't have been parsed as an outline.

Fix some polarities in `ChordData`. Add `bearing1` and `bearing2` to allow more convenient arc drawing on canvas.

Omniblox/Eagle-Loader,Omniblox/Eagle-Loader,Omniblox/Eagle-Loader