Separated execution and user interface logic, preparing for a GUI.
Some Javadoc fixes and additions.
Added a graphical UIObserver, still not functional.
Added a graphical interface.
Still pending error check, about, etc.
Run console UI by default, and graphical through command line parameter
-gui.
Added about message in graphical UI.
Validate user input for cutoff in graphical UI.
Run graphical or console UI depending on parameters and (lack of) system
console.
Merge branch 'gui'