turn on nitpicking

docs/conf.py

@@ -72,7 +72,7 @@
 
 # If true, Sphinx will warn about all references where the target cannot
 # be found.
-# nitpicky = True
+nitpicky = True
 
 # A list of (type, target) tuples (by default empty) that should be ignored when
 # generating warnings in "nitpicky mode". Note that type should include the