integration: add ModuleDoc and AutoDoc
It is important to be able to document modules other than CSRs.
This patch adds ModuleDoc and AutoDoc, both of which can be used
together to document modules.
ModuleDoc can be used to transform the __doc__ string of a class into a
reference-manual section. Alternately, it can be used to add additional
sections to a module.
AutoDoc is used to gather all submodule ModuleDoc objects in order to
traverse the tree of documentation.
Signed-off-by: Sean Cross <sean@xobs.io>