Overhaul to be more OO

[RangerMauve]

I've rewritten a bunch of Webrun so that it's more OO and more plugin-friendly. Closes #7

• Create a class that encapsulates setting up the environment and loading modules
• New plugin system
  • Plugins are functions that take a webrun argument. They can do whatever they want to it from there
  • Plugins are capable of using addProtocol("protocol:", async (url) => String to add a protocol handler
  • Plugins can use addGlobals((currentglobals) => newglobals) in order to plug into the setup process where globals are being set up.
• Default class that extends Webrun and provides a set of plugins
  • Browser globals
  • Node integration (require, self.onmesage, self.postMessage, self.close)
  • Dat (dat: protocol, DatArchive API)
  • FIle (file: protocol)
  • HTTPS (https: protocol)
• Reworked how stuff is loaded so that the process will exit by default unless you use something dat-related. This means that tests don't need to rely on self.close() for stuff to be cleaned up. In the future we can probably get by with using archive.close() on archives to clean up resources, and stopping the swarm when everything is done.
• Reverted some of the child_process functionality because it was messing up the REPL and removing autocomplete and other such features.
• Added the cli arguments functionality. Now if I run webrun something.js --foo bar it'll append ?foo=bar to import.meta.url. Closes #1
• self.postMessage now stringifies content that isn't a string
• Tests are broken at the moment, but manual testing has been promising

[RangerMauve]

That's pretty much how it is! If you don't use Dat, then Dat won't take up the event loop and it'll exit normally.

The reason that loading a DatArchive or something from a Dat URL keeps the event loop alive is that it opens up a socket for replicating the content.

I'm 100% sure what the best approch is for this yet, so far I'm thinking that it'd make sense to count the number of places actively using a dat archive, and once it's no longer needed (using the .close() API), it'll stop replicating that archive. Once all archives are closed, I could stop the discovery swarm portion and have it woken up again after another DatArchive is loaded.

I don't think this needs to be addressed for this PR, however, so I think I'll leave it as a TODO for now.

[RangerMauve]

Changed how addGlobal behaves so that all globals that plugins add are lazy-loaded. 😀