Fantastic plugin!
As a chess fan myself, I am really happy that you've created this. The plugin works really well and the design is very nice.
There are only 2 things however that I would like to be added/changed:
1) I was checking to see if you got all the chess rules right; and you have missed one:
https://lh4.googleusercontent.com/KBpBCY2GtlNmM-EkcEuuxHe3Bb0aePAJOMCV8bVsnCdypvHZv_UAEldqDe3pNdrUoUeqB8N-wDAvEVedHvJJ6i26aZlvCO4Fftorao0johknLKpf52aM7hWxy_bgK8hszTvL45Gm
This image shows the one you missed. As you can see, the black bishop guards the f1 square, which is on the king's way to castle, therefore it is illegal in this situation, for the king to castle (sorry about being so bratty about chess rules but it bothers me a lot).
2) I want there to be a rotate option for the board. I think it is currently set up that all boards face north. If there was a way to rotate the boards, that would be awesome.
Besides those two things, you did an amazing job. 10/10