Split saturnin-demo to a double-package distribution, where one package
provides core saturnin-demo with its subcommands and the other provides
a Shellfu/Bash module saturnin_demo_greet.sh used by the first one.

It's GPLv2, really.

Tests are supposed to set it on their own and not rely on environment.
Hence it's not even interesting to have in TF_HEADER.

This requires newer Saturnin version in order to avoid bug where
SATURNIN_CONF_PATH environment variable would be ignored.

Several changes to improve maintainability, readability and style of
packaging meta-data:

 *  Use more maintainable syntax in templates.  That is, more MKit macros,
    line-based lists, etc.

 *  Use Markdown for LICENSE.

 *  Use normal case (don't YELL) in application name.

 *  Use only spaces to align spec file.

 *  Use version ranges for SemVer dependencies.

 *  Sort %files section.

 *  Use shorter version level (0.y vs 0.y.z) in ranges where possible

 *  Move MKit compatibility directive to bottom (which actually changes
    the compatibility level to 0.0.24 as older MKit had a bug that
    prevented seeing the directive near the bottom.)