MAINT: fix up numpy.testing port

- remove clearly outdated stuff (KnownFailureException, import_nose, datetime support etc)
- fix up imports from numpy to torch_np --- in *some* functions.
ATM, things which are exposed in `torch_np.testing` via `__init__.py` are OK, the rest isn't.

Author: ev-br

torch_np/testing/__init__.py

@@ -0,0 +1,6 @@
+from .utils import (assert_equal, assert_array_equal, assert_almost_equal,
+        assert_warns, assert_)
+
+from .testing import assert_allclose    # FIXME
+
+

torch_np/testing.py renamed to torch_np/testing/testing.py

@@ -1,6 +1,6 @@
 import torch
 
-from ._ndarray import asarray, asarray_replacer
+from .._ndarray import asarray_replacer, asarray
 import torch_np as np
 
 @asarray_replacer("two")