ENH - (Windows) Support aas_expandpathbyvars for Windows

[AljenU]

Currently aas_expandpathbyvars does nothing on Windows. Thus paths in the xml cannot use environment variables like %APPDATA%.
Should path expansion also be supported on Windows? Does need to take into account also #288

The subfunction expandind would change from

ind = sort([strfind(x,'$'),strfind(x,'`')]);

to e.g.

if ispc()
    % Even more unsafe than on non-pc, since % is likely to be found in formatting expressions
    ind = sort(strfind(x,'%'));
else
    ind = sort([strfind(x,'$'),strfind(x,'`')]);
end

[tiborauer]

It is not a core goal but is worth noting as a TODO for later.
However, it seems you, @AljenU, have already found a clever solution. :)

[AljenU]

It basically works indeed. However, because the % is also used a lot in printf formatting statements, there is even more chance of accidental replacements (#288). Thus i would be more comfortable if there were some improvements for #288

[tiborauer]

How about using $ for Windows, as well? I know it is not a direct mapping and might be a little confusing for the users, but some explicit documetation would help for sure.

[AljenU]

On windows, there needs to be a % at the start and at the end of the environment variable that is to be replaced. So the analogy with the unix case would get even more confusing.
And to deviate from standard conventions should have a really good reason, since it is easy to accidentally fall back to default behaviour, which would then lead to errors.
I did just add some idea for fixing #288, in which case it would also be ok to enable this one with the easy change from the starting comment.