Wasm support?

[jgarvin]

I don't see any mention in the README, but would be sweet to have given the library's aspirations.

[ispringle]

I think we would need to do something similar to the example in the wgpu-rs repo. From my limited understanding and use of this, we need to provide a means of linking the the Canvas if we're compiling for wasm. winit does most of the work, just would need to setup the option. I think the ideal way to do it would be to add this to directly to coffee so that you can just specify a target and cargo will compile it.