Implement custom headers

[vmorkovyn]

Need to know, from which frontend received request by websocket call. I think, it would be great, if we have opportunity to mark routes in swindon config by label and then get label from header in each request.

[tailhook]

Any reason why extra-headers doesn't work?

[popravich]

extra-headers only work for static files.
I guess we can make this setting common to all handlers.
Your thoughts?

[tailhook]

Yes. Just be careful not to replace content-length or transfer-encoding headers.