Improve bash autocompletion script

[PT-15]

Fixes #71

[nikolassv]

Thank you so much for your contribution! I'm really sorry for the delay in getting back to you.

I really like the idea of enhancing autocompletion. Unfortunately, the current script expects the bartib file to be located at /opt/shared/bartib-hist and throws an error if it doesn't exist. Would you be able to fix this? Perhaps you could check for the BARTIB_FILE environment variable first, and if it's not set, simply disable the description autocompletion.

[PT-15]

Hi! Sorry for the delay, these months have been crazy.
Thanks for the feedback, I think that should fix the problem. I also added a few autocomplete options that were missing.