We were calling always the cargo script to build all, on each call to
build but we can provide the rs input and let meson to check if some
source has changed and if not, it won't try to build.
I've added the env var CARGO_HOME pointing to target directory to make
it cacheable when you build Fractal with builder to speed up building.
I've also added an env var check to difference between DEBUG mode and
RELEASE mode so you can configure GnomeBuilder to build the debug
version.
This script creates a new release, increasing the release number in all
files then it creates a new commit and the creates a new tag, and
finnaly it generates the .tar.xz release file.
