* On the web, load different maps by making asynchronous HTTP calls. #21
This is a very strange, specializd approach; it's unclear how it'll
generalize to reading scenarios and prebaked results. Ideally we could
call abstutil::read_binary as we currently do and somehow hide this async
trickery underneath, but I'm not sure how yet. In the meantime, this
moves us forward with the hack well-contained.
Next steps for web: stop bundling in all of data/system in the .wasm,
now that we can load from HTTP.
When I added web support in February, it was easier to get started with
stdweb, since it has the nice cargo web tool. However, stdweb is
unmaintained, winit is deprecating support for it, and the next steps
for web (downloading maps dynamically) have better support for web-sys.
With Alvin's guidance, I got
https://github.com/dabreegster/minimal_websys_winit_glow_demo working
first. This PR cuts A/B Street over too.
I tested abst and the widgetry demo in both native and web. The only
major regression from stdweb is the canvas placement and size. I
attempted some fixes, but at this point, I'll leave it as a smaller
followup instead.
