Add security notes
Add new symbol :hard to modify :sub

By default, categories listing (and :sub) will ignore all forbidden categories.
Because the permission of an album in Piwigo does not fully inherit its parent
permissions, the Piwigo behavior may prevent some new sub-albums from being
accessible by group members. See for example
   http://piwigo.org/forum/viewtopic.php?pid=137575#p137575
By using this directive :hard, all forbidden categories are unhidden, hence
this almost override settings from Piwigo system. This may lead to confusion
and some difference between Piwigo settings (via WebConsole) and this plugin.
However, let us see how it helps.
Add FIXME
Merge branch 'hard_sub'
update doc
Merge branch 'hard_sub'