re-structure SS7 code and MGW NAT code into separate modules

This repository now only contains the SS7 code
diff --git a/rebar.config b/rebar.config
new file mode 100644
index 0000000..10d55cf
--- /dev/null
+++ b/rebar.config
@@ -0,0 +1 @@
+{sub_dirs, ["rel"]}.