HTTP request handling

[cceckman]

Given a failure to parse an HTTP request (#3), reset the connection.

Given a parsed message (#3), figure out whether it matches a set of routes, and trigger the response for whatever route was matched.

• GET with static content
• GET with side effects and dynamic content (hit counter)
• POST to LED
• Something with GPIO?

If it doesn't match, produce an appropriate response:

• No matching host: 400 Bad Request
• No matching URL: 404 Not Found
• Matching URL, but not method: 405 Method Not Allowed
• Accept has no Content-Type match: 406 Not Acceptable (...or just ignore it, "default representation" is an option)