Netty 4.0.24.Final 发布

Netty 4.0.24.Final 发布，此版本关闭了 54 个任务/issues，是重要的修正版本。此版本是之前 4.0 系列的临时替代版本，趁还热乎，感觉尝尝鲜～

重要的 bug 修复和改进：

#3058 #3057 - SslHandler - DirectByteBuffer - OutOfMemory
#3031 - 禁用 SSLv3.0 来避免 POODLE 漏洞
#2971 #2972 - WebSocketClientProtocolHandshakeHandler 泄漏
#2965 - Avoid vectored writes for small websocket messages
#2964 - zero-sized DefaultFileRegion leads to system stuck & high sys usage
#2955 - 提升 WebSocket 性能
#2940 - 为客户端 websocket 子协议添加认证
#2924 - head is not updated when trim MemoryRegionCache
#2880 - HTTP Content Decoder Cleanup Bug
#2871 #2867 - Workaround performance issue with IPv4-mapped-on-IPv6 addresses
#2860 - Add support for gathering writes with native transport when using EpollDatagramChannel
#2855 - Disable caching of PooledByteBuf for different threads
#2831 - Modify HttpObjectDecoder to allow parsing the HTTP headers in multiple steps
#2823 - Writing DefaultFileRegion with EpollSocketChannel may cause hang
#2789 - Allow efficient writing of CompositeByteBuf when using native epoll transport
#2586 - AbstractBootstrap.bind(...) should use correct EventLoop to notify on late registration