xonsh: update to version 0.14.1 (#9294)

Also:

- Fixed tab-completion when using libedit.
- Avoid mentions of "~/.xonshrc". Point to, and use,
~/config/settings/xonsh/xonchrc instead.
- Added "pygments" as a required package.
It is listed as an optional dependency, but "xonfig web"
(a command user will likely try as it is advertized at
start-up) fails without it.
- Silenced a startup error message, as it is known to be a
libedit vs readline issue, and doesn't seems to affect
normal usage.

Will now warn against using libedit, and recommend installing
the "gnureadline" Python module instead (currently, we don't
have it on HaikuPorts).
- require prompt_toolkit now that we have it. It provides
a much more richer experience out of the box.