Added a check to ensure all contacts in a set exist
Changed the type of error thrown by addNewPatMeeting if one of the
contacts doesn't exist
Added a test that checks if all the contacts in a Set exist
Added a comment to the constructor
Added the code to the flush procedure to write the contents of the class
to a text file
Added the test for the flush procedure
Added a procedure to search for past or future meetings based on a
contact. The procedure is consolidated in to one to avoid code duplication
Replaced the java.util.* import statement with more specific statements