Mass rename indices->indexes.
Rename indices file.
Missed feeds in mass renaming.
Make feeds a subclass of indexes. Cleanup!
Remove dead code in PAGE-URL.

We partially support 'pretty URLs'. They can be achieved by setting
:page-ext in the *config* to "/" and configuring the web server to
ignore html extensions.
Move CONSTRUCT into util, it's more general than CONTENT.
Generalize DO-CTYPES to DO-SUBCLASSES, update callsites.
Alphabetize config slots, docs TODO about content types.
Update theming docs and README a bit.
Fix FEEDS definition thinko and tweak some more docs.
Remove feeds from defsystem.
Initial pass at the Document Protocol.
Massive indexes rewrite.
Miscellaneous fixes.
Sitemap plugin tweaks.
More comments and docs tweaks.
Template linking fix.
Rename index-posts -> index-content.
Update templates to match posts->content.
Factor purge-all calls in discover to a before method.