ikiwiki/ todo/ beef up sidebar to allow for multiple sidebars

Maybe sidebar could be beefed up to take the name of a sidebar, such that I could use multiple sidebars in the same wiki. For instance, the default name would be 'sidebar', meaning the plugin looks for sidebar.pm and fills in the sidebar slot, but I might also want a footer in footer.pm, filling the template's footer slot.

One good way (if possible) would be to provide a directive like [[!sidebar id=sidebar]] which would cause the file, in which it occurred to fill the slot SIDEBAR in the template: basically, a page foo.mdwn says [[!fillslot slot=myslot]] and then its contents should go into <TMPL_VAR SLOT_MYSLOT> for all pages. Ideally, this can then be overridden, so if /bar/foo.mdwn also references myslot then pages under /bar should get those contents instead.

--madduck