Release checklist for Tux Paint Stamps

Places to make sure version # and release date gets updated, prior to
cutting a release (tagging in the source code repository, and running
"make release" to roll a .tar.gz source tarball).

 * Build description files:
   * tuxpaint-stamps.spec.in (RPM packages)
   * win32/tuxpaint-stamps.iss (Windows installer build)
   * macOS installer build (via XCode)

 * Documentation
   * docs/CHANGES.txt
   * docs/README.txt

 * Update stamp descriptions (.txt files) to sync with translations
   * Follow the "README.txt" directions in the "po" subdirectory

Also:

 * Make sure "android_packager/build_for_android.sh" accepts
   all locales for which translated description audio files
   are available (see the usage output of the script, it finds
   them dynamically).
