Separate more functionalities

Now if you use the block you will still execute a lot of useless hook and node_api functions.

If we think the module as:
- One simple filters than add the id to headers.
- One token than display the toc (using real drupal token, in core in D7). And eventually an associated filter
- One block than display the toc of the current node
- Perhaps one field than display the toc

It become pretty simple no? those 4 functionnality can be in seperate modules with in the main module only the function than provide a toc.