Add --concise about acleanbib

[Olamyy]

Fixed part of this.

Use a conference short code ("In Proc. ACL") instead of the default long booktitle "In the Proceedings of the Nth Annual Meeting...")

The above part seems a bit difficult to get around at first look so I'm going to look at it again tomorrow.

The particular issue is around the booktitle entry in the bibtex.
A typical booktitle could be "Proceedings of the 54th Annual Meeting of the Association for Computational Linguistics".
There's however no way to match this to an exact venue in the venues.yaml. At least5 different venues match this booktitle.