WIP: Add convergence scripts

This is the convergence script that I used for EWASS. It produces the following plot:

Let me know if you don't think it's appropriate to be added in this way.

examples/SodShock_1D/convergence/README.md

+Convergence Testing with the Sod Shock
+======================================
+
+The scripts in this folder are used to test the SodShock for convergence.  Due
+to the requirement of recompiling with different hydrodynamics schemes, the
+`./run_convergence.sh` script will actually clone the whole repository from the
+GitLab.
+
+These tests may take a couple of hours to run, so be careful! They are not
+something that you want to run on your laptop.