library: Bridge the remainder of the API

[shazow]

• type ResponseWriter
  • Write
  • WriteHeader
  • Header
• type Request
  • Method
  • URL
  • Host
  • Header
  • Body (io)
  • ... Bunch of other stuff we may or may not care about?
• type Server
  • API for a straight-up handler or a custom Server configuration?
• Other stuff?