Support tag links and "tagged with" page.

[endel]

I've spent a little time adding some tag functionality, such as links to tags for each article, and a "tagged with" page.
I think it is pretty cool for the main project.
endel@a62a199

You can see it in action here: http://bugfixer.endel.me/2011/04/19/animate-spritesheets-with-imagemagick/

[dreamr]

It would be really swell if this was tested ;P

I like the feature, and I am working on tests now. I am new to riot, and trying to figure out simple unit tests :)

[ixti]

I have prepare my own version of tagging support, see #90. I hope it will cover all needs. Will appreciate your thoughts and comments.