Per RFC 7230 Section 5.4 mandate that all requests contain a Host header

Technically the RFC only mandates the host header for HTTP/1.1
requests however due to the widespread adoption and the importance
of the Host header for virtual hosting we'll mandate the header
for HTTP/1.0 connections as well.
Merge pull request #1 from dstufft/mandate-host-header

Per RFC 7230 Section 5.4 mandate that all requests contain a Host header