Let `\author` and `\set{author}` be equivalent

[paolobrasolin]

Currently,

• \author targets only direct LaTeX compilation and
• \set{author} targets only AsciiDoc conversion.

Merging their behaviour is complicated by the fact that their syntax for multiple authors is very different, and a non trivial amount of tex and xsl code would be needed.

This could be a nice feature but since we're targeting primarily AsciiDoc conversion I think it's not urgent due to its complexity; furthermore, the problem can be circumvented pretty easily by using both macros in the preamble:

% for a single author
\author{John Doe}
\set{author}{John Doe}
% for multiple authors
\author{Tom Sawyer \and Dick Tracy \and Harry Potter}
\set{author_1}{Tom Sawyer}
\set{author_2}{Dick Tracy}
\set{author_3}{Harry Potter}