Simple libevent2-based http server for Mono

Hello. I've extracted code related to libevent from Nancy.Hosting.Event2 and tried to create a test for it.

cat results/checkit/20131012001008/json/evhttp-sharp/raw |grep Requests
 Requests/sec: 22959.18
 Requests/sec: 30499.05
 Requests/sec: 23004.14
 Requests/sec: 25774.58
 Requests/sec: 28083.28
 Requests/sec: 28963.05
 Requests/sec: 29389.00
 Requests/sec: 30680.66

And a bit better results for plaintext. It doesn't consume 100% CPU (don't know why, I even use several worker threads for evhttp), but I think these results are the best ones that we can get for Mono.

http://paste.ubuntu.com/6224868/ - test log
https://github.com/kekekeks/evhttp-sharp - sources (multiworker branch). I'll implement a host for ServiceStack based on this code later.