v0.4.0

Refactor:

• Rename event_loop() to loop() of EventLoopThread/TCPClient/http::Service
• Rename libevent_watcher.{h,cc} to event_watcher.{h.cc}
• Rename evnsq::ConnPtr to evnsq::NSQConnPtr

Bug fix:

• Fix unit test failed problem. If the tcp_client_thread does not start,we do TCPClient::Connect, that will cause race-condition problem #25
• Fix file descriptor leak bug #23
• Fix TCPServer::Stop coredump #26
• Fix HTTP Server::Stop coredump #27 #28 #29 #36
• Fix TCPServer::HandleNewConn assert error and fix a race condition problem of TCPServer::Start #30
• Fix DNSResolver will invoke callback twice when it is timeout #32
• Fix evnsq Client::IsReady() implement wrong #21