Babelviscofdtd

Fixed bug with domain size calculations in CUDA when no mini kernels are used (the default mode for CUDA)

Fix an issue with the mapping of unique values when attenuation is used. It could cause some divisions by zero

A CMakeLists.txt file was missing

A lot of simplifications allowed having a much more straightforward code. Thanks to Andrew Xie (IAmAndrewX) for a very productive summer trimming down code, replacing the old MTLPP with Swift, and making a new class arrangement for the different GPU backends. Now BabelViscoFDTD is based completely on PyOpenCL and PyCUDA for the FDTD viscoelastic solver. For Metal, the Swift-based wrapper does the interfacing. The old C extension is still around just for the OpenMP backend.

The MTLPP C++ library is now replaced by a Swift interface to access the Metal implementation for the viscoelastic FDTD solution. This will ensure using a more standard Apple development language for the future, as MTLPP is not maintained anymore. While there is a new Apple-based C++ wrapper for Metal, using Swift is still preferred as we created now a C-linking compatible library that in the future can be also used directly in Python. In the long term, we aim to eliminate the C code extension and use only Python code in tandem with pyopencl, pycuda and Metal.

Thanks to some exchanges with the Apple Engineers in their Developers forums, some refined implementation of the main kernels was done where the computations are split in "mini-kernels". All Metal-based tests showed an increase in performance.