"Plugins" are bundles of tiddlers managed as one, "modules" are
JavaScript tiddlers with a module type identifying when and how they
should be executed.
Now there is now longer a dummy DOM element corresponding to the macro
itself. Instead, macros must create a single element child. This allows
us to more easily fit Bootstrap's requirements for HTML layout (eg,
that problem with links in navbars not being recognised). The
refactoring isn't complete, there are still a few bugs to chase down
