Proof of concept: publisher-subscriber model for asset loading

[mggower]

• large graphs were experiencing errors because too many promises were being emitted simultaneously
• a publisher-subscriber model for asset loading reduces the amount of async loading is required
• this approach is non-blocking, so things like text will use default fonts before a font asset is loaded by the browser which speeds up the initial paint

[mggower]

couldn't think of a better name for this method lol

[mggower]

TODO: plug in to Renderer options

[jameslaneconkling]

Let's try the loader pattern I mentioned here and see if that helps. The Async function (which is really just a callback with some bells/whistles to make it feel more like a promise) is more lightweight than a promise, so might not have the same issue.