support protocol relative base url

[thenewguy]

Just tracked down a problem with ogvjs after our url parser output was adjusted. Getting this error: Uncaught (in promise) TypeError: Failed to execute 'fetch' on 'WorkerGlobalScope': Failed to parse URL from //foo.example.com/path/to/ogvjs/ogv-decoder-audio-vorbis-wasm.wasm?version=1.8.6-20220111172545-1f60d9d

It would be handy if protocol relative urls were supported for the base url