made RAG public and hyperlinked networkx.Graph documentation

skimage/graph/__init__.py

@@ -1,6 +1,6 @@
 from .spath import shortest_path
 from .mcp import MCP, MCP_Geometric, MCP_Connect, MCP_Flexible, route_through_array
-from .rag import rag_mean_color
+from .rag import rag_mean_color, RAG
 from .graph_cut import cut_threshold
 
 __all__ = ['shortest_path',
@@ -10,4 +10,5 @@ __all__ = ['shortest_path',
            'MCP_Flexible',
            'route_through_array',
            'rag_mean_color',
-           'cut_threshold']
+           'cut_threshold',
+           'RAG']

skimage/graph/rag.py

@@ -37,7 +37,8 @@ def min_weight(graph, src, dst, n):
 class RAG(nx.Graph):
 
     """
-    The Region Adjacency Graph (RAG) of an image.
+    The Region Adjacency Graph (RAG) of an image, subclasses
+    `networx.Graph <http://networkx.github.io/documentation/latest/reference/classes.graph.html>`_
     """
 
     def merge_nodes(self, src, dst, weight_func=min_weight, extra_arguments=[],