New variable SATURNIN_META_HELP can be used to control what happens when
user calls the meta command with `--help` argument.

conf is Saturnin's internal command to access common configuration.  It
could be, in theory, useful for end-user to investigate the configuration,
but they would already need to know how it works and which configuration
keypaths or sections they want to look at.

Bettter hide it; it's not worth for the potential confusion.

Note that the command could actually even be removed one day since
internally it's much more efficient to use saturnin__conf().

Overview of changes:

 *  Properly filter subcommands on listing

    In contexts like main --help and tab completion, Saturnin would show
    also arbitrary files from libexec that did not start with dedicated
    prefix ($SATURNIN_LIBEXEC_PREFIX).  This was a mistake and was never
    intended to work that way.

 *  Hook code is now run as separate bash process

    Running it within sub-command code was a little bit too unsafe;
    there's no need to be evil^Weval here.

 *  Rewrote saturnin__version() (used for app --version)

    Newly, --version will only incorporate tagline if it was defined in
    mkit.ini.

    Also "Powered by Saturnin" line has been added so that we don't have
    to ask user every time.

 *  Added --saturnin-get-saturnin-version

    It's a good idea to include this with test reports and the like so
    we're making it more accessible to scripts.

 *  API documentation clarifications

 *  Codebase maintenance

 *  Refactoring for code readability

Only print tagline if defined (similar to codename); do not make it up
with silly string.

Also we can do away without any local variables *and* very safely inside
79 character width recommendation.

eval was little bit too much.

This was always intended; sub-commands starting with dedicated prefix
is the mandatory convention.

As recommended by Shaturnin style guide:

    https://github.com/AloisMahdal/shellfu/blob/master/notes/style.md

As recommended by Shellfu style:

    https://github.com/AloisMahdal/shellfu/blob/master/notes/style.md

Overview of changes:

 *  Added generic config file finder

    This can be used to find config files other than INIs but using the
    same merging mechanism.  For example, `saturnin__conf_find "foo"`
    should output to first existing instance of file "foo", which could
    live under any of paths set in SATURNIN_CONF_PATH (typically
    /usr/share/app/ini.d/dist/foo, /etc/app/foo, ~/.config/app/foo,
    ~/.config/app/ini.d/my/foo...).

    This function is now also internally usef by saturnin__conf().

 *  Added module-version meta-data for future Shellfu generations

    Current version of Shellfu does not support this yet, but in future
    it should read this and display in lists, man pages, etc.

This should be useful for cases when a sub-command wants to maintain
non-INI config locations.

Overview of changes:

 *  Added saturnin__bug() to help developers help users report bugs
 *  Tweak debug output regarding some globals
 *  Fix document packaging 'doc'
 *  Infrastructure maintenance

The related functionality is stable already and the path is easy to find
out using package manager.

Overview of changes:

 *  Converted to pure shellfu library

    So far we have relied on users embedding Saturnin inside their app
    and updating it by porting changes manually.  This has been awkward
    but was safer for preliminary versions where feature set was not
    stable and separation of the library and the app skeleton has not
    been done properly.

    Nowadays, these problems have been mostly resolved; the feature set
    seems to be stable and the app skeleton has been reduced to only the
    few lines, so it's time to make Saturnin a proper shellfu library.
    Of course, Saturnin can still be embedded, but primary use case is
    to depend on it and import it just as any other shellfu module.

    The 'satcmd' demo app has been moved to a different repo.

 *  Ported conf merge tests from old inigrep

    This was a long-standing debt from the inigrep split.  Tests
    originally created for inigrep have been ported to focus on
    saturnin__conf(), throwing few more in for good measure.

 *  Enabled --help (friendly usage()) in saturnin__conf()

    saturnin__conf() (exposed to user as `myapp conf`) now supports the
    obligatory --help argument.

 *  Did some updates and cleanups.

Move satcmd to other repo and distribute saturnin as a stand-alone
shellfu library.  Users can import just the library instead of
embedding it inside their source tree, which enables them to delegate
part of the job to package manager.

We're scratching right ear with left hand...

 *  Fixed bug that prevernted saturnin_conf queries to contain spaces

Absence of quotes breaks queries with spaces.  We're already taking care
of files (implicit or given on command line).

Overview of changes:

 *  Don't hide short options from usage message and Bash autocomplete
 *  saturnin-conf now has usage message
 *  saturnin-conf now exits with useful status in some scenarios
 *  Hacked completion code together so that updating should be easier
    (command name is set only once)

 *  Cleanup and maintenance

Overview of changes:

 *  Improved help and usage messages

    Small but long wished for change; this may improve ability to
    explore apps easily.

 *  Code clean up and maintenance

Will make code less ugly at places.

Be nicer to people who get help by trial and error.

Overview of changes:

 *  Updated for shellfu 0.9.x

    New shellfu version brings about a lot of changes; this release is
    mostly about catching up with it.

 *  Use predictable meta binary name

    Applications will have updating easier if they use simple generic name
    for meta-command source file; we should set an example (that's the
    point of satcmd, after all).

 *  Minor clean up