Added a new decorator for simplifying the creation of templatetags that span over a block of nodes ({% foo %} ... {% endfoo %}). This does all the hard, redundant work of parsing the parameters, figuring out which are optional, setting up the class, and resolving variables. The implementation just has to render the content. This greatly simplifies our tags implementation.

The change to the templatetags will be posted under a separate review.

Converted several tags to use the new blocktag decorator. Some of the tags have a fixed number of required arguments, while others have optional arguments. All worked.