fix plugins to work with jinja2 renderer

[willkg]

The jinja2 renderer doesn't do cb_head, cb_foot, cb_story, ... callbacks. Many of the plugins require these to work properly.

They should be updated to add things (variables, functions, ...) to the context so that they can be used in templates.

[willkg]

Breaking this down into steps:

1. remove all the cb_head, cb_foot, cb_story, ... stuff.
2. create a cb_context_processor callback that lets plugins add functions and variables to the Jinja2 environment.
3. rewrite plugins that use the old blosxom callbacks to use the new context_processor callback.
4. document new context_processor callback.

This has some interesting ramifications on how plugins work.

For example, the tags plugin used cb_head and cb_foot and added a variable that built a list of all the tags for the blog. Instead, it can add an object to the context that has:

1. a list of (tag, tag url, count) tuples for all tags on the blog 2.. a function that generates HTML for a generic tags list which probably covers most peoples' needs
2. a function that generates HTML for a tag cloud
3. a function that takes an entry and returns the tags for that entry as a list of (tag, tag url) tuples
4. a function that takes an entry and generates HTML for a generic tags list which probably covers most peoples' needs

[willkg]

I like the new system a lot better.

Plugins to rewrite

• [x] tags
• [x] paginate
• [ ] archives
• [x] categories
• [x] draft_folder
• [x] ignore_future
• [x] pages
• [x] published_date
• [x] rst_parser
• [x] yeararchives
• [x] readmore (probably going to get rid of this one)

[willkg]

For clarification, I folded the interesting bits of readmore into rst_parser and ditched the readmore plugin.

[willkg]

The last one to rewrite is archives. I'm going to close this issue out and open a new issue to merge archives and yeararchives into a datearchives plugin.

[willkg]

Done! Yay!