url parsing and formatting utilities

[odino]

from @omissis

sounds like we need require('@url') 🙂

[odino]

I want to take this issue as a way to introduce building native modules in Go -- eg. currently the entire stdlib modules are written in ABS but eventually to expose a bunch of functionalities (like crypto) we should allow doing so in Go. I don't know how exactly we should do this, but the URL example seems an "easier" one.