1. Download and include CPM.cmake, version 0.42.0
2. Use CPM.make to get Pybind11
3. Update to use pybind11=3.0.0
4. Also use CPM to configure/build nvbench
Make it explicit in README that we build and locally install NVBench first,
and then build Python package use the library as a dependency.
The nvbench library is installed into Python layout alongside the native
extension.
Edit wheel.packages metadata to include namespace package "cuda".
Updated README to remove the work-around of setting PYTHONPATH,
as it is no longer necessary.