Edits for code_skeleton branch in amanabt/DG_Maxwell

[Balavarun5]

The command 'af.set_backend(sys.argv[1])' gives an error while execution. Setting backend to opencl solves this. The test_waveEqn should contain tests for only the basic functions. eg:- A matrix is different for 2D case and hence the test written for 1D can't be used.

[amanabt]

Sorry, I forgot to explain you the change.
Initially, we were doing af.set_backend in all the files wherever we were importing arrayfire.
The problem was that when we wanted to change the backend, we were bound to change it
in all the files. To get around this issue I started taking command line arguments.

So, you were supposed to run the program like this:

python3 main.py <backend>

Here, sys.argv[1] will store the backend you will enter while executing the program.

This was, however, a temporary solution and we cannot keep doing this because we are building
a library and so, we cannot take command line arguments.