To make easier to do an unattended slackpkg update/upgrade process,
this commit provides different exit codes to many situations:
0 Successful slackpkg execution.
1 Something wrong happened.
20 No package found to be downloaded, installed, reinstalled,
upgraded, or removed.
50 Slackpkg itself was upgraded and you need to re-run it.
100 There are pending updates.
Code and the main manpage are updated accordingly.
In addition, this commit also:
- removes the ChangeLog.txt in doinst.sh, so the needed
'slackpkg update' after Slackpkg upgrade won't says it's all OK
and don't need to redo the package lists
- removes AUTHORS from manpage. Nowadays there are code from many
people in Slackpkg and shows a bit unfair to have only my and
Evaldo's name listed there.
Signed-off-by: Robby Workman <rworkman@slackware.com>