Underscore does not seem to be allowed in Debian package names.

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.

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.)