Introduce a new `brianobj` role that allows easier linking to Brian
objects.
Call sphinx without using `os.system` -- allows for debugging and
sphinx-build does not have to be in the path.
Correctly display trailing parentheses for method names
docstring fixes: do not use :meth:, :class:, etc. -- we always want to
use our `brianobj` role
Fix duplicate listing of class attributes in the "Attributes" table of a
class.
Add a mechanism to document a subset of all preferences.
Add some more flexibility to the preferences documentation, allow
documenting the same preference in more than one place.
Use the brianobj role in "See Also" etc. as well.
Fix tests (remove sphinxext test which did not really test our own
extension)