Add SDC extension for numba (#253)

Remove support numba_python tests for numba<0.46
Removed numba_pandas package and tests. Move extension point to hpat/__init__.py

hpat/__init__.py

@@ -35,3 +35,12 @@
 
 __version__ = get_versions()['version']
 del get_versions
+
+
+def _init_extension():
+    '''Register Pandas classes and functions with Numba.
+
+    This exntry_point is called by Numba when it initializes.
+    '''
+    # Importing SDC is already happened
+    pass

setup.py

@@ -528,4 +528,10 @@ def run(self):
       install_requires=['numba'],
       extras_require={'HDF5': ["h5py"], 'Parquet': ["pyarrow"]},
       cmdclass=hpat_build_commands,
-      ext_modules=_ext_mods)
+      ext_modules=_ext_mods,
+      entry_points={
+          "numba_extensions": [
+              "init = hpat:_init_extension",
+          ],
+      },
+)