Wrapper around three main functions from pretty.sh.  Useful to
demonstrate modularity of pretty.sh, eg:

    PRETTY=color saturnin-yell warn "you're doing it wrong"

will print the warning colored in the terminal, but

    PRETTY=color saturnin-yell warn "stop right now"

will send a desktop notification instead.

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.