support for alternate ring-compliant servers

[trevor]

Would it be possible to use ring-compliant servers aside from jetty?

• https://github.com/weavejester/ring-server/blob/57567629a896c83f6a7c7961f8070496036070db/src/ring/server/standalone.clj#L100

If so than it may be possible to use lein-ring with http-kit:

• https://github.com/http-kit/http-kit
• https://github.com/http-kit/chat-websocket

[trevor]

related: weavejester/lein-ring#65