flup is not supported on Python3, so MediaGoblin doesn't have a supported way to enable FastCGI support.
This change removes all references to flup and FastCGI and updates deployment instructions to use simple HTTP forwarding with nginx to access mediagoblin's non-static resources.
* create initial bits for plugin writer's guide
* move siteadmin stuff to site administrator's guide
* rework index.rst to support multiple guides
* tweak some text
* move files into subdirectories
I verified that this still works with html and texinfo build targets.
There's still a lot of work to do, but this is a good start.
