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.
The new Shellfu brings some large changes. Among what touches us
directly:
* Most global variables were renamed (removing SHELLFU_* prefix).
* inigrep API has been revamped and the file merging/guessing
feature has been dropped; it now belongs to us.
subcommand (binary) and its arguments are both already is debug-shown
inside saturnin__runsc; cases when that does not get called are normally
not interesting.
Scripts may need it (eg. if using `saturnin__runhook()`) but exporting
it in the middle of main script makes it harder to see the scope
clearly and also is ugly.
Tweak the saturnin__runsc syntax so that it's not dependent on this
being global and export the SATURNIN_SUBCOMMAND only for the actual
subcommand binary call.
This module is intended to be moved around with saturnin, but unlike
main meta-command (bin/saturnin.skel), it should not be necessary to
rename it or edit to adapt to new project.