This will be needed by the next commit to display an "About" dialog via
the corresponding entry in the app menu that will be added.
This also adds the PACKAGE_URL, PACKAGE_VERSION and VCS_TAG
configuration data.
* Preliminary documentation of CallsCall and CallsMessageSource
* Documentation and cleaning up of CallsCallData
* Add data files and meson rules to create gtk-doc documentation
* Move some macros from util.h to calls-message-source.h