I don't often use graphics applications. I sometimes use GIMP to do simple things like resizing and cropping. So I'm not the best person to comment on the features and the end result.
However I can comment on technical stuff.
In the VCS repository (bzr), I see that some generated files are present, like the configure script, install-sh, etc. The best practice is to never add in the VCS generated files, only the source files. When using the Autotools, that means adding only the conifgure.ac and Makefile.am files. When compiling from the VCS, instead of running ./configure, there is generally an autogen.sh script.
Until recently, for GNOME modules there was gnome-common, but gnome-common has been deprecated in favor of the autoconf-archive. See:https://wiki.gnome.org/Projects/GnomeCommon/Migration
You'll see an example of autogen.sh script there. Various GNOME projects already follow that, see for example the gspell
library (look at the Git repo).
I'm writing a GLib/GTK+ tutorial
for the C language (still incomplete). Comments welcome.