demo/cgofull: add multi cgo module and macro calling

_demo/cgofull/pymod2/pymod2.go

@@ -0,0 +1,11 @@
+package pymod2
+
+/*
+#cgo pkg-config: python3-embed
+#include <Python.h>
+*/
+import "C"
+
+func Long(l int64) *C.PyObject {
+	return C.PyLong_FromLongLong(C.longlong(l))
+}