* Move most documentation out of the ulab base module.
* float -> _float
* ulab.ndarray -> ulab.numpy.ndarray
This still does not build unless it is taken together with a modification
to CircuitPython that _also_ moves references to ulab.numpy.
Because of this, this PR will continue to show red. The suitability of
the changes can be gaged by looking at the related CircuitPython PR build
or by running locally the build-cp.sh script with the right ref checked
out in circuitpython/
