moved validation into InstructionMessage constructor so can be accessed with default add() method
fixed typo in docs
renamed addInstruction to overloaded add() method
updated readme
added docs to InstructionMessage
added high/low test, doesnt even compile due to incomparable
added getPriority, compareTo and toString methods to InstructionMessage
passing high/low, med/low, high/med test. essentially testing priorityqueue class methods, so maybe shouldve tested InstructionMessage methods instead
edited doc comments
All tests passing, all features working, merging branch f_comparator into develop
fixed readme with last checklist item