v0.17.1

There have been quite a few (including backward incompatible changes) since the first "public" release.

Among a few important changes:

• preliminary support for OpenBSD and FreeBSD; (on FreeBSD one requires fdescfs mounted on /dev/fd;)
• improve support for Python3+ scriptlets;
• add support for custom z-run executable for a particular library;
• add support for z-run --shell (that runs bash with a custom bashrc), as well as z-run --export=shell-rc or z-run --export=shell-functions, plus the few embedded prologs;)
• add support for embedded --help manual;

Plus many other smaller fxups, updates, features or improvements.

This release requires Go 16.1 as it uses the newly introduced embedding facility.