Help: Add documents to collect notes between releases

Add a release/dev.txt file and include it from release/index.rst in
development versions.  Add a "Changes Since Release" section with a
toctree that globs adjacent "dev/*" documents.  Add a sample topic
document explaining how topic-specific release note documents work.

This approach will allow developers to write release notes for their
changes as they are made.  The release manager may then consolidate and
organize the notes for a specific release version.

Help/release/dev.txt

@@ -0,0 +1,16 @@
+..
+  This file should be included by the adjacent "index.rst"
+  in development versions but not in release versions.
+
+Changes Since Release
+=====================
+
+The following noteworthy changes have been made in this development
+version since the preceding release but have not yet been consolidated
+into notes for a specific release version:
+
+.. toctree::
+   :maxdepth: 1
+   :glob:
+
+   dev/*

Help/release/dev/0-sample-topic.rst

@@ -0,0 +1,7 @@
+0-sample-topic
+--------------
+
+* This is a sample release note for the change in a topic.
+  Developers should add similar notes for each topic branch
+  making a noteworthy change.  Each document should be named
+  and titled to match the topic name to avoid merge conflicts.

Help/release/index.rst

@@ -1,6 +1,12 @@
 CMake Release Notes
 *******************
 
+..
+  This file should include the adjacent "dev.txt" file
+  in development versions but not in release versions.
+
+.. include:: dev.txt
+
 Releases
 ========