setup.py: add -funroll-loops option

setup.py

@@ -9,7 +9,7 @@ setup(
     Extension("groupConnectivity",
       sources = ["groupConnectivity.pyx"],
       language="c++",
-      extra_compile_args=["-std=gnu++11", "-O2"]
+      extra_compile_args=["-std=gnu++11", "-O2", "-funroll-loops"]
     )
   ])
 )