Directories can now have Readme files, called ((__readme)). Readme
files are injected into pages via the new renderer ((inject::readme))
(probably the first of several injectors).

The current templates don't inject ((__readme)) in normal directory
views, but do inject them for blog and blogdir views (as you may see
from this directory). Blog and blogdir views now drop all files
starting with ((__)), taking out ((__readme)) and ((__access)) and any
future special magic files.

{{CutShort}}

This is perhaps a lame approach that ChrisSiebenmann will rethink
later. The general problem is however quite real, and is at its root
two problems:
* different pages of the same type + view sometimes need to have
  somewhat different contents. The differences can come from either
  (or both) the page hierarchy or the template hierarchy, but they
  have to come from somewhere.
* while useful templates can be hard to write, so even with the
  ability to specify what template a view + page combination is
  rendered in saying 'put the differences into a custom template' is
  not necessarily a satisfactory answer.

Some sort of 'injection' support to add content to pages under some
circumstances seems useful in general. It's possible the long run
solution will be injecting full template pieces instead of just
injecting wikitext content from the page area.

(This all somewhat implies that much content positioning will be done
by CSS, since that makes content much easier to inject without
changing lots of things around it.)