examples: add a simple self contained tcp echo server

examples/tcp_echo_server.v

@@ -0,0 +1,35 @@
+import net
+
+// This file shows how a basic TCP echo server can be implemented using
+// the `net` module. You can connect to the server by using netcat
+// or telnet, in separate shells, for example:
+// `nc 127.0.0.1 12345`
+// `telnet 127.0.0.1 12345`
+
+fn handle_connection(con net.Socket) {
+	if _ := con.send_string("Welcome to V's TCP Echo server.\n") {
+		for	 {
+			line := con.read_line()
+			if line.len == 0 { break }
+			eprintln('received line: ' + line.trim_space())
+			con.send_string(line) or { break }
+		}
+	}
+	con.close() or {}
+	return
+}
+
+fn main() {
+	server_port := 12345
+	eprintln('Starting an echo server, listening on port: $server_port')
+	server := net.listen(server_port) or {
+		panic(err)
+	}
+	for	 {
+		con := server.accept() or {
+			server.close() or {}
+			panic(err)
+		}
+		go handle_connection(con)
+	}
+}