added GreatestCommonDivisor.java and will make the program have more than one method in GreatestCommonDivisorMethod.java
Merge remote-tracking branch 'origin/master'

Conflicts:
	CollegeBook/src/Methods/GreatestCommonDivisor.java
Merge remote-tracking branch 'origin/master'

Conflicts:
	CollegeBook/src/Methods/GreatestCommonDivisor.java