Merging visibility configuration changes from CS15 Repo. This includes the addition of 4 new configuration options for visibility (as we previously had for just Valgrind) corresponding to the 4 other tests that are created by make_gradescope_results.py. In particular, the total score, style, token, and build tests.
This merge request includes changes to code (autograde.py, make_gradescope_results.py) and documentation (README.md).