New Plugins

Added some plugins to the list of available plugins.

• Hop Nguyen wrote a Who's online? script and a hit counter
• anand wrote MostPopular, LatestComments and TopRated (well, actually they were written a while back, but they were not listed on the plugins page yet)

Also, I plan on releasing v1.55 somewhere next week. It will mainly contain fixes for some bigger and smaller problems that were in v1.5. Next to that, it'll have some small improvements and additions.