Add request header routing

[techwraith]

It would be great if Barista allowed us to match routes based on the request's headers. It would help a lot when allowing custom domain support.

router.match('/').where({headers: {host: 'somesite.com'}})

[kieran]

While Barista has no knowledge of the request itself (nor do I think it should, separation of concerns etc...), I could certainly hack in a way of matching arbitrary params, then Geddy would pass in a hash of whatever as a third parameter for matching.

[techwraith]

That would work for our use case :)