Lots of documentation changes

* added a YouCanHelp directive to replace FIXMEs and encourage contributors
  to help out
* moved some bits around between the hacking howto and the codebase documents
* expanded on the stub nature of the theming howto
* tweaked some other text

docs/conf.py

@@ -16,7 +16,7 @@ import sys, os
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
-#sys.path.insert(0, os.path.abspath('.'))
+sys.path.insert(0, os.path.abspath('.'))
 
 # -- General configuration -----------------------------------------------------
 
@@ -25,7 +25,7 @@ import sys, os
 
 # Add any Sphinx extension module names here, as strings. They can be extensions
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
-extensions = []
+extensions = ["mgext.youcanhelp"]
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']