3.24.2: (stable)

* PO-files: added: why `fuzzy` tag appears
  (DarkTrick) Merge request !14
* Update the "Working with gtkmm's Source Code" appendix
* index-in.docbook: Upgrade from DocBook 4.5 to DocBook 5.0
* Recommend Meson instead of Autotools
* "The .hg and .ccg files" section: Describe 'ignore_deprecations'
  (Kjell Ahlstedt)

Meson build:
* Require Meson >= 0.56.0
* Don't require gtkmm unconditionally
* Specify 'check' option in run_command()
* Don't use gnome.yelp()
  In Meson >= 0.61.0, it can't be used with a generated XML file.
* Add allow-network-access option
  (Kjell Ahlstedt)