Release version 2.68 to avoid users from running into fixed issues

[joe4dev]

Users run into unnecessary problems that were actually fixed but not yet "released" because they download/compile older code:
For example, bibtool -x myfile.aux is broken in 2.67 but actually fixed in HEAD: https://tex.stackexchange.com/questions/499320/problem-with-bibtool-when-extracting-bibliography-information-from-an-aux-file-i
Currently, even users following the download instructions on Github will get an outdated version (e.g., from CTAN or your website).

At least officially tagging it on Github would make it more convenient to install (e.g., through Homebrew).

[ge-ne]

done