http4s/http4s — pull request #94 by julien-truffaut (2014-11-29 19:45:40+00:00)
Title: Add type classes to encode a query parameter

This PR is not ready yet, I just wanted to use it a proof of concept for #86 and get your feed backs.

Ideally I would use 3 type classes:
* one to encode a type T to a `QueryParameterValue`
* one to decode a `QueryParameterValue` to T (with potential of failure)
* one to describe the parameter key associate to a T

The decode and encode type classes should satisfy basic encoding laws:
* for all t, decode . encode == success