Changes to "meta" file in START

[mjpost]

I am hoping we can get START to make some changes to the meta file. These apply to all current conferences (e.g., ACL 2020):

Remove:

• "Type" (type): no longer used
• "Bibtex URL" (bib_url): no longer used

Add:

• "Short book title" (key shortbooktitle), with the example "Proceedings of WMT"
• "Volume name" (key volume), with the default example "TOBEFILLED: volume number or name within collection"

CC: @rrgerber

[mjpost]

The ACLPUB "master" branch now expects these new fields, and no longer uses bib_url. I have tested it locally, but I haven't merged it into the "start" branch yet, because it should first be tested there.

@rrgerber, how should we go about this? Do you want me to merge it into START, and then you test it? Or will you test first before merging into START?