New APIs

• DTLS supports, we can build WebRTC applications now (#3188) (@matyhtf)
• Built-in FastCGI client, we can proxy HTTP request to FPM with one line of code now (swoole/library#17) (@twose)
• Co::wait, Co::waitPid, Co::waitSignal (#3158) (@twose)
• Co::waitEvent (#3197) (@twose)
• Co::set(['exit_condition' => $callable]) to set exit condition of reactor (#2918) (#3012) (@twose)
• Co::getElapsed to get the coroutine elapsed time (#3162) (@doubaokun)
• Socket::checkLiveness, Socket::peek (#3057) (@twose)
• Socket->setProtocol(['open_fastcgi_protocol' => $bool]) (#3103) (@twose)
• Server::getInstance, Server::get(Master|Manager|Worker)Pid, Server::getWorkerId (#2793) (#3019) (@matyhtf)
• Server::getWorkerStatus (SWOOLE_WORKER_BUSY, SWOOLE_WORKER_IDLE) (#3225) (@matyhtf)
• Server->on('beforeReload', $callable) and Server->on('afterReload', $callable) (Server reload event on manager process) (#3130) (@huanghantao)
• Http\Server support http_index_files and http_autoindex with static handler (#3171) (@huanghantao)
• Http2\Client->read(float $timeout = -1), support Coroutine\HTTP2\Client read more than once (#3011) (#3117) (@twose)
• Http\Request->getContent (alias of rawContent) (#3128) (@huanghantao)
• swoole_mime_type_(add|set|delete|get|exists) (mime APIs) (#3134) (@twose)

Enhancement

• Optimize memory-copy between master and worker (4x faster) (#3075) (#3087) (@huanghantao)
• Optimize websocket dispatch (1x faster) (#3076) (@matyhtf)
• Optimize memory-copy in websocket_construct_frame (1x faster) (#3097) (@matyhtf)
• Optimize SSL validation (#3226) (@matyhtf)
• Separate SSL accept and SSL handshake (#3214) (@twose)
• Support MIPS (#3196) (@ekongyun)
• Support CURLOPT_FAILONERROR (swoole/library#20) (@sy-records)

Remove

• Remove Runtime::enableStrictMode method (b45838e) (@twose)
• Remove Buffer class (559a49a) (@twose)

Kernel

• New C++ API: coroutine::async with lambda (#3127) (@matyhtf)
• Refactor event API and reactor fd to swSocket (#3030) (@matyhtf)
• Convert all source files to C++ (#3030) (71f987f) (@matyhtf)
• Code optimizations (#3063) (#3067) (#3115) (#3135) (#3138) (#3139) (#3151) (#3168) (@huanghantao)
• Code optimization for header files (#3051) (@matyhtf)
• Refactor enable_reuse_port option (#3192) (@matyhtf)
• Reactor Socket API (#3193) (@matyhtf)
• Reduce one system call (3b5aa85) (@matyhtf)
• Remove swServerGS::now (#3152) (@huanghantao)
• Improve protocol setter (#3108) (@twose)
• Use the Better way to init C object on stack (#3069) (@twose)
• Use type uchar for bit field (#3071) (@twose)
• Support parallel test (#3215) (@twose)

Fixed

• Fixed enable_delay_receive (#3221) (#3224) (@matyhtf)
• Fixed ConnectionPool->fill (swoole/library#18) (@NHZEX)
• All other bug fix patches have already been merged into the v4.4.x branch, we will not reiterate them here