Add custom opencl

Add a custom operator implementation on OpenCL Backend.

• User can give the OpenCL code snippet to be used within an OpenCL ElementwiseKernel.

hysop/operator/tests/test_custom.py

@@ -155,8 +155,6 @@ class TestCustom(object):
             print(' *has_inf: {}'.format(has_inf))
             print(' *dinf={} ({} eps)'.format(dinf, deps))
             print()
-            print(fout[:, 3, 4])
-            print(fref[:, 3, 4])
             msg = 'Test failed for {} on component {} for implementation {}.'.format(iname, i, impl)
             raise RuntimeError(msg)