Catch-up with git version tags

* update debian/changelog
* update TODO-RELEASE
* add comments to Makefile.am and TODO-RELEASE to simplify the process
  in future
* add link to libtool docs to Makefile.am to simplify LIBVERSION
  maintenance

Related: OS#1861
Change-Id: I22c257e357f597519120232d742d6a61289db021
diff --git a/TODO-RELEASE b/TODO-RELEASE
index 17f6521..fb0bfea 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -1,7 +1,9 @@
+# When cleaning up this file: bump API version in corresponding Makefile.am and rename corresponding debian/lib*.install
+# according to https://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html#Updating-version-info
+# In short:
+# LIBVERSION=c:r:a
+# If the library source code has changed at all since the last update, then increment revision: c:r + 1:a.
+# If any interfaces have been added, removed, or changed since the last update: c + 1:0:0.
+# If any interfaces have been added since the last public release: c:r:a + 1.
+# If any interfaces have been removed or changed since the last public release: c:r:0.
 #library	what			description / commit summary line
-libosmogsm	internal API update	Internal API for GPRS cipher implementors updated to accommodate for arbitrary key lengths
-libosmocore	change major	external talloc dependency / internal talloc removal
-libosmocore	change major	size of ph_data_param struct changed / Extend L1SAP PH-DATA with presence information
-libosmocore	change major	size of ph_data_param struct changed / Extend L1SAP PH-DATA with measurement information
-libosmocore	change major	size of ph_tch_param struct changed / Extend with RTP Marker
-libosmocore	change major	size of struct log_target changed / Extend with GSMTAP