Braille Code Metadata: do we need a dedicated field for the braille code revision?

There are some examples of entries in the [list](https://github.com/daisy/ebraille/wiki/Braille-Code-Metadata-Rules-&-Terms#rules-for-braille-code-metadata) that have a year in them, e.g. Danish codes have a "1993" and a "2022" version. In Liblouis (on which the initial list is based), we decided to keep separate tables for some of the older revisions, such as the 1993 version of Danish braille, because they are still in use, and we didn't want to force everyone to use the 2022 revision of the code right away. There are however potentially much more braille code revisions that could be included in the list. Liblouis is a braille translation software that doesn't need to support every braille code that ever existed. But it could be a different story for eBraille: it is a file format that could potentially be used for archiving.