Add python3 doc building capability

doc/tools/apigen.py

@@ -200,7 +200,7 @@ class ApiDocWriter(object):
         classes : list of str
             A list of (public) class names in the module.
         """
-        mod = __import__(uri, fromlist=[uri])
+        mod = __import__(uri, fromlist=[uri.split('.')[-1]])
         # find all public objects in the module.
         obj_strs = [obj for obj in dir(mod) if not obj.startswith('_')]
         functions = []

doc/tools/build_modref_templates.py

@@ -25,7 +25,7 @@ if __name__ == '__main__':
 
     try:
         __import__(package)
-    except ImportError, e:
+    except ImportError as e:
         abort("Can not import skimage")
 
     module = sys.modules[package]