New exit status for different situations

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>

0 files changed, 0 insertions, 0 deletions