ADDED: Kerr metric
REMOVED: unnecessary breaks from Schwarzschild metric code.
FIXED: Added forgotten header
MODIFIED: Particle class now has more virtual functions
ADDED: Draft of Entity class
ADDED: Proper derivative calculation for Entity class.
Moved the engine into a separate directory
Removed readme from branch engine.
FIXED: Some fixes.
Merged branch 'engine' into tests
Adjusted the tests to new file paths.