Add performance improvements to configuration and handler lookup

These changes increase the performance of Sanford by preparing
hosts before they are used in the server. This is done in the
new `PreparedHost` class. A host's configuration is merged with
optional overrides and it's configured service handlers are
constantized. This removes overhead from a request's lifecycle,
which translates into increased performance.

Closes #33
Update to use the new Sanford-Protocol

This adds the speed improvements in the latest protocol (v0.5.1)
with Sanford's own.