State of GtkSourceView 4

Hi,

Ignacio wondered about the state of GtkSourceView 4 (still depending on
GTK+ 3, to rename the namespace from GtkSource to Gsv).

See:
https://wiki.gnome.org/Projects/GtkSourceView/RoadMap

To rename the namespace, a script is missing to fix the code formatting
in headers, following the GNOME conventions.

Also, I've decided that I don't care about GTK+ 4 (for now). So as far
as I'm concerned, there is still plenty of time to care about
GtkSourceView 4 and 4.9x. I anyway do that work without being paid, so
the bare minimum is that I can choose what I do, and currently I prefer
developing the Tepl library.

If anybody else cares more about GtkSouceView 4 and 5, contributions
welcome!

--
S=E9bastien