Previously, apigen documented all but the bottom-most level of modules in the package tree. This caused problems when different subpackages had different depths. Instead, just document subpackages (ignore python files, whose public functions should already be loaded into the subpackage).
Documenting inherited methods and attributes can lead to overly verbose docs. For example, the `Image` class, which subclasses ndarray, and various viewer-related classes, which subclass PyQt and Matplotlib classes, have hundreds of irrelevant methods added to the API docs.
Either the role should be removed (as done here) or the inheritance-diagram extension needs to be added to the config file. Since skimage doesn't have a complicated class hierarchies, it's probably best to remove.
__import__ can get confused about which scikits path to import when multiple scikits are present on a system.
Note that `root_module` is no longer an attribute of `ApiDocWriter` (it wasn't being used anywhere), and it now points to "scikits.image" instead of "scikits".
Stefan van der Walt