src: use itty-router for routing requests

[flakey5]

Closes #122 Closes #106 Closes #111

TODO

• [x] r2 middleware
• [x] origin middleware
• [x] caching middleware
• [x] tests
• [x] commenting
• [x] custom request type (contains parsed url so we only do it once)

[flakey5]

cc @ovflowd