* Allow single dimension slices in mgrid and ogrid

* Use requirements.txt and pin black version

* Update black formatting

* use sphinx section names

* Generalize the type interface to tensor.zeros and tensor.ones

* Add axis argument to squeeze

* remove optimization from ScalarSigmoid.c_code()

Remove the optimization from ScalarSigmoid.c_code(), as it was incorrect and did not optimize much. Add test case that passes without that optimization and failed with it.
Co-authored-by: Brandon T. Willard <brandonwillard@users.noreply.github.com>
Co-authored-by: Oriol (ZBook) <oriol.abril.pla@gmail.com>