... turns out it's faster (surprise! ;))

Due to inigrep limitation, we cannot automatically cherry-pick hook.ini
based on where the hook is found--we can only have all hooks in one
file, or use join strategy.

Add section like this to hook.ini:

    [hook.mycomm]
        pre = echo $SATURNIN_SUBCOMMAND will run soon
        pre = echo $SATURNIN_SUBCOMMAND is almost running
        post = echo $SATURNIN_SUBCOMMAND has finished now

"@" breaks the string to several arguments, which is not what we want
here

Config files can now be merged from 4 sources:  distribution-provided,
(share folder), local (/etc/saturnin), user-specific (~/.saturnin and
~/saturnin/ini.d/*)

Paths are transferred by saturnin meta-command so there's no need
to build sub-command binaries

Move cub-command to libexec path to prevent calling them directly,
allowing for better control of environment.