Split docs into siteadmin and pluginwriter guides

* 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.

docs/source/index.rst

@@ -11,29 +11,42 @@
    Dedication along with this software. If not, see
    <http://creativecommons.org/publicdomain/zero/1.0/>.
 
-.. GNU MediaGoblin documentation master file, created by
-   sphinx-quickstart on Thu Apr  7 20:10:27 2011.
-   You can adapt this file completely to your liking, but it should at least
-   contain the root `toctree` directive.
 
+===========================================
 Welcome to GNU MediaGoblin's documentation!
 ===========================================
 
-Table of Contents:
+Part 1: Site Administrator's Guide
+==================================
+
+This guide covers installing, configuring, deploying and running a GNU
+MediaGoblin website.  It is written for site administrators.
 
 .. toctree::
-   :maxdepth: 2
+   :maxdepth: 1
 
-   foreword
-   about
-   deploying
-   production-deployments
-   configuration
-   media-types
-   help
-   relnotes
-   theming
-   codebase
+   siteadmin/foreword
+   siteadmin/about
+   siteadmin/deploying
+   siteadmin/production-deployments
+   siteadmin/configuration
+   siteadmin/media-types
+   siteadmin/help
+   siteadmin/relnotes
+   siteadmin/theming
+   siteadmin/plugins
+   siteadmin/codebase
+
+
+Part 2: Plugin Writer's Guide
+=============================
+
+This guide covers writing new GNU MediaGoblin plugins.
+
+.. toctree::
+   :maxdepth: 1
+
+   pluginwriter/foreward
 
 
 Indices and tables