A simple multiworker http server using event-driven. I just want to take it as
my own network programming practice.

Main thread forks some worker threads, wait for request and dispatch requests
to workers.

Now it supports only GET and HEAD.

It uses http_parser and libevent. Because http protocol RFC2616 is so tedious,
I cannot read all. And I plan to replace libevent with a simple event lib
written by myself, in order to practice. I now use libevent for convenience.

A simple introduction about the orgin version, which only used a single worker,
can be found at:
    http://blog.csdn.net/tricky1997/article/details/7438242
This version has added the multiworker support.