* Fix image path names in GTK+3 gresource files
Turns out it cares about the whole path, not just the filename, even
if you embed the pixdata.
* Fix change_color.sh following autotools changes
* Add --jobs option to change_color.sh to pass to make
This defaults to nproc.
* Update HACKING document following autotools changes
* Note in README which engines require sassc, optipng, and inkscape
5444ac751f