Allow passing ROM URL as a querystring parameter

[qguv]

Hi! I'm using wasmboy's embed feature to create little pages that let you play builds of a game I'm working on. But these lack the ａｅｓｔｈｅｔｉｃ and don't behave great on mobile.

It would be neat if I could instead create a vaporboy link like https://vaporboy.net?rom_url=https://qguv.github.io/undercooked/releases/undercooked_v0.0.5.gb (or if cors is a problem, https://qguv.github.io/undercooked/vaporboy.html?rom_url=releases/undercooked_v0.0.5.gb) that would load the rom from a given url.

[torch2424]

@qguv Thanks for the issue! 😄

Oh yeah! I could totally add the same functionality to vaporboy once I have the time! 😄