Add a Doxyfile and preliminary module-level docs.

src/ssb.rpc.h

@@ -1,6 +1,15 @@
 #pragma once
 
+/**
+** \defgroup ssb_rpc SSB RPC
+** Implementations of all the necessary MUXRPC handlers (createHistoryStream,
+** ebt.replicate, blobs.get, ...).
+** @{
+*/
+
 typedef struct _tf_ssb_t tf_ssb_t;
 
 void tf_ssb_rpc_register(tf_ssb_t* ssb);
 void tf_ssb_rpc_start_periodic(tf_ssb_t* ssb);
+
+/** @} */