fix: memory leak (#279)

add wrap on data too

fix #273

added Control() function to give user privilege to set net.PacketConn

add NewConn4 to let user delegate the conn to UDPSession to close

bump xorsimd to add linux/loong64 support (#270)

awesome

do not reserve in kcp core, reserve bytes in callback func

fix recycle

add a depicted ASCII graph for general flow of the session

add license to source codes