Adjusts spacing of characters in Car.java
Implements Car.toString() and Car.getColor() to pass CarTest.canDoToString()
Adjusts spacing of characters in CarTest.java
Adds new test in CarTest.java named canDecelerate()
Implements Car.setSpeed() and Car.decelerate() to pass CarTest.canDecelerate()
Adds new test in CarTest.java named cannotDecelerateBelowZero()
Updates Car.decelerate() to pass CarTest.cannotDecelerateBelowZero()