Refactor CMake Setup

[BlaiseMuhirwa]

This change refactors CMake project setup and hopefully make is less confusing by breaking down different components into separate files. I created a cmake folder where we can put re-usable CMake code. For instance, we currently have cmake/FindAVX.cmake, cmake/FindZLIBAndCNPY.cmake and cmake/FindGoogleTest.cmake. This is a standard way of organizing a large CMake codebase.