Removed dependencies on pandas and cython.

[albop]

@cc7768 , @sglyon : there has been some pep-ification behind my back, but what the actual part of this PR:

-    # TODO  do we need a pandas grid here?
-    grid = pd.lib.to_object_array_tuples(points).astype(float)
+    grid = np.array(points)

It seems like a no brainer to me but I also don't understand why you used pandas in the first place. Do you remember it ?

Otherwise we can remove pandas and cython as dependencies.

[cc7768]

I don't know why we used pandas to do that operation -- Seems silly of us to have done that.

Additionally, it seems like all tests still pass and it simplifies the code/dependencies, so I'm in favor of this change.

[albop]

Thanks. Just wanted to be sure. I'll merge that one then.