feat(c/libuv): Add tcp, udp, poll, core, stream, err features

feat(c/io): add libuv async io with io, tcp, udp, timer, dns, loop

feat(c/io): add libuv async io with stream, req, handle

feat(c/libuv): rename c/io to c/libuv, and improve errro, net, handle, stream

feat(c/libuv): Add a libuv demo: echo_server

refactor(c/libuv): Adjust comments and file names to accommodate merge

c/net/net.go

@@ -91,10 +91,23 @@ type SockaddrIn struct {
 	Zero   [8]c.Char
 }
 
+type SockaddrIn6 struct {
+	Len      uint8
+	Family   uint8
+	Port     uint16
+	Flowinfo c.Uint
+	Addr     In6Addr
+	ScopeId  c.Uint
+}
+
 type InAddr struct {
 	Addr c.Uint
 }
 
+type In6Addr struct {
+	U6Addr [16]uint8
+}
+
 type SockAddr struct {
 	Len    uint8
 	Family uint8