Merge zx-adaptations

[uwiger]

This PR brings zx-related adaptations into master. zx/zomp documentation.
This has some effect on the release process.

gproc is published in the uwiger realm (realm file).
My intention is to set git version tags that follow the version control in zx, so the release process will be:

In zx:

$ zx verup [major | minor | patch]
Version changed from 1.0.1 to 1.1.0.
$ make

(after testing, checking in and pushing to github)

$ ./zompify.sh
$ cd [packaging-directory]
$ zx package [path_to_gproc]/_build/zomp/lib/gproc
$ zx submit uwiger-gproc-1.1.0.zsp
$ zx approve uwiger-gproc-1.1.0
$ zx accept uwiger-gproc-1.1.0.zsp

After this, we can tag the commit with git tag -a 1.1.0 -m "1.1.0" and release to hex.

Note that building with rebar3 works just like before. The zompify.sh script cleans up a rebar3 build for zomp packaging.