Extend the character limit on the `citations.author` column

[ashiklom]

It should be possible to add a complete list of authors to the authors column. Such a list is obtainable from the rcrossref package functions, among other things.

Currently, the limit of 255 characters on the author column is way too restrictive. While importing citations from the TRY database, I came across papers with a complete author field that is 1110 characters long.