Fix a CI failure

Fix source wheel builds

In the previous release, building from source wheels got you the wrong
version number. That has now been fixed.

Fix build script

Building after cloning was sometimes failing in 3.6.6.

Parse Guile command lines

Cred to @daym in #131!

Make setup.py generate px/version.py

Back to how it used to be. This fixes a brew build failure.

Rethink handling of future processes

Before this change, during both testing and runtime we asserted on
processes created in the future.

Since this randomly failed in CI, and possibly for some users as well,
those checks have now been moved to local testing only. Note that I
have been thinking about this but never managed to figure it out, so
hiding it is my best bet for now...

Improve command line parsing

Specifically of zsh scripts and brew.sh invocations.

Special handling for the Dart language binary

Unindent everything one notch

Not fully correct, but since PID 1 has only one parent indenting it
doesn't add much information, but does use up space, so let's just not.

ptop: Add a tree mode

With this release, if you press `m` (change sort order) twice, you will
get to see the process tree. It's sorted by aggregated CPU usage.

Requested here:
#124