[RiccardoRossi]

📝 Description

this PR adds a semi explicit CFD solver which can either run on the CPU or GPU. Myself and @rubenzorrilla we have been working on this for quite a while and it is currently in a reasonable state.

it requires the library cupy and pyamg

python3 - m pip install cupy 
python3 -m pip install pyamg

The solver is entirely written in python but leverages blas calls to be efficient.
With the current version and using a mid-tier GPU it is about 10 times faster than the gpu.
Having said this, honestly the style is a good fit to the gpu but probably not for use on cpu. Efficient and parallel use of the CPU will depend on the undetying blas.

user can set gpu or OpenMP as:

    "problem_data": {
        "problem_name": "Drywell_CFD_Only",
        "parallel_type": "gpu", //"OpenMP"
	"precision" : "float32",
        "echo_level": 0,
        "start_time": 0.0,
        //"end_time": 0.02
        "end_time": 4.0
    },

[roigcarlo]

sorry for the force-push noise :S