Multi-processing

[sjacks26]

Add multi-processing. Users should be able to specify the number of concurrent processes or utilize all processors.

[sjacks26]

References:
https://medium.com/@bfortuner/python-multithreading-vs-multiprocessing-73072ce5600b
https://sebastianraschka.com/Articles/2014_multiprocessing.html
https://timber.io/blog/multiprocessing-vs-multithreading-in-python-what-you-need-to-know/