Merge pull request #39 from eve-val/feature/spoiler-tags

Invert the polarity on spoilers +/- button
Handle 0-threads case in is_forum_read (fixes #40)

This fix both the problem that empty forums show as unread, and the
error after marking an empty forum as read.
Merge pull request #41 from eve-val/unread-indicator-bugfix

Handle 0-threads case in is_forum_read (fixes #40)
Don't try to mark thread read for anonymous users.
Merge pull request #43 from eve-val/unread-indicator-bugfix

Don't try to mark thread read for anonymous users.
Spoiler bbcode tweaks

 - rename [spoilers] to [spoiler] since that seems to be more standard.
   Hopefully no one is depending on this too much yet.
 - strip leading & trailing whitespace inside spoiler tags. I'm not sure
   whether this is standard, but I definitely think it is better.