Feature: MPI parallel

[HPDell]

Add MPI paralleling support for gwr_basic() and gwr_multiscale().

This is not a parallel mode with in R code via setting the parallel_method parameter (this is used to specify the method used in each kernel). To enable MPI mode, follow these steps

• Install MPI SDK and runtime. On Linux/macOS, the OpenMPI is tested. On Windows, the Microsoft MPI is tested.
• Install Rmpi following the official instructions.
• Write an R script to calibrate a model. Don't forget to save the model in a file.
• Use the following command to run the script.

mpiexec -np <number of processes> Rscript <path to script>

MPI is supported by SLURM system, so it can be easily used on a high performance cluster.