Preparations for testing (i.e. bugfixes and tests).

1. Tested all CLI arguments.
 -r: works
 -tu: works, but misses slightly when not using -cdt (lasted for 1000661.99303 universe seconds, should have lasted for 1000000.0)
 -tr: works, but misses slightly (lasted for 12.0107421875 real seconds, should have lasted for 12.0)
 -f: works
 -s: works, has to be redone
 -dts: works
 -cdt: works
 -fe: works
 -cnt: works
 -se: works
 -min: works, has to be benchmarked

2. Fixed the -s flag (now uses universe time instead of number of updates).
3. Tested -fx against -min: -min is about 16 times faster!
4. Found hypothetical CLI arguments to use during research: "solar_system -s x -r 60 -tu y -cdt z -fe -min"
5. Created the tests/ directory.
6. Created the benchmark.py framework.
7. Created the time benchmark and found out Graviton can simulate the universe around 3701 times faster with cdt=1.