Starting GpuCumsum
Add a dummy kernel for testing.
First draft of the cuda cumsum.
Fix durp error
Fixed bugs, added some unit tests.
Make cumsum recursive to handle very large array
Added more tests
Cumsum 2D in cuda is working when axis=1.
Add a 2D version cumsum
Cleaned code and unit tests
Adressed comments from @abergeron and @nouiz

Added __eq__ and __hash__ methods.
Fixed c_code_cache_version
Check if axis=None before bailing out.
pep8
make test pass when device=cpu (this is the normal)
Add tests for different strides.

Fix one problem related to strides by copying the strides infos
from the input to the output.
Force float32 tests and use the mode for gpucumsum tests
pep8
Disable the perform on the gpu op.
Assert that the gpuop is used.
smaller test size
Force cast of dim3's attributes to int.