It makes a lot of noise that is normally not very relevant to the
application.

They made sense when the script was bigger, now they delimit basically
the whole script.  Also "built part" is not accurate since the part is
not built--it only happens to contain lot of macros.

Saturnin Shellfu module used to be embedded into the repo; now it lives
its own life (we already have it in dependencies).  All the app needs is
meta-command and scripts.

Overview of changes:

 *  Fixed quoting when setting $SATURNIN_CONF_PATH

 *  Replaced complete.bash with skeletal version of itself

    With reasonable version of mkit, the skeleton can be readily used
    without any modifications.

 *  Applied first attempt to be more conformant with XDG standards

    Saturnin-demo now uses XDG paths for cache, local data and config
    data and does it in such a way that respects these values from
    environment variables as prescribed by current XDG.

    Note that not all paths described by XDG are used.

 *  Simplified Saturnin's mkit tokens

    Another step to increase usability of this demo with as little
    modifications as possible.

(Shame I did not see that earlier...)

First attempt to base saturnin paths on XDG paths.

Turns out this is not good practice; the tokens are only used within the
process of building the application so there's no need to qualify them.
Having them qualified in fact adds unnecessary spam when syncing with
the template.