Add swaymsg subproject

swaymsg/main.c

@@ -0,0 +1,11 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+void sway_terminate(void) {
+	exit(1);
+}
+
+int main(int argc, const char **argv) {
+	printf("Hello world!");
+	return 0;
+}