Add support for additional client/server adapters

[ptaoussanis]

Sente currently supports #{:clj :cljs :node} servers and #{:cljs :node} clients.

To add support for an additional server, a small adapter needs to be written. In most cases, the adapter should be pretty easy to write.

See:

• Instructions on how to write an adapter
• Examples of current adapters

Otherwise feel free to ping with any questions. Cheers! :-)