My initial submission for Challenge 4

I believe I am performing this pull request successfully.  I had issues getting the pull request to work properly on Challenge 2, but it seems to be working this time.

I haven't had time to convert the app into Swing, so this will need to be ran from the IDE Console of choice, or the command prompt.  If running from the command prompt, make sure to build the class correctly using javac before running it directly.

Example:  javac ExpressionSolve.java
Execute:   java ExpressionSolve