First prototype

The prototype should be functional, although there might be some bugs.
It should be able to retrieve a list of thread IDs in a Google Group,
and use it to download all the whole threads as returned by the server
(in pb+json format).

Change-Id: I434321a2db96a6e983d27b69b86efd5abebe7618
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..f012df5
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module gomodules.avm99963.com/google-groups-takeout
+
+go 1.16