Merge pull request #1 from kumpelblase2/master

Changed cylinder input to float
Add clock and tests.
Merge branch 'tim' of https://github.com/kumpelblase2/RubyUniversityExercises into tim
Add ability to subtract time
Changed minute and hour constants to local. Added some documentation for clock.
Merge pull request #2 from kumpelblase2/tim

Add clock