Remove Prince and Frog chess piece types.

The Prince and Frog were added to the project to fulfill course
requirements. Since this is now my project, and I just want a working
chess game, I've removed them.
Remove manual test plan doc.

I never really finished the test plan. It's also inaccurate now that I
have removed "Frog"s and "Prince"s. The test plan was also more course
work baggage that didn't need to be in my version of the app.
Remove game start image.

The game start reference image is inaccurate since I removed the "Frog"
and "Prince" type chess pieces.
Update license date.
Add File enum for constants.

I added preliminary support for creating chess pieces using standard
algebraic chess notation. The File enum allows me to set a chess piece's
column with a letter. I haven't added any tests or examined the various
subclasses of ChessPiece to add support for this new enum yet.
Rename hasValidStartingPosition to inValidStartingPosition
Add comment to explain why enum was made.
Add support for File enum to King.

This expands support for the File enum to the King class, so I can give
positions in algebraic chess notation. I reorganized some of King's
tests and added some new ones. I still need to add/update a few more
tests.
Update King's tests.

This finishes the changes I needed to make to King after adding the File
enum. I also made general improvements to the test code. This change
also adds a (file, rank) move function to ChessPiece.
Add isValidMove common code to ChessPiece superclass.

Every chess piece's isValidMove method ran the same check to determine
if the new position is on the board and not the same as the current one.
Since this property needs to happen in every subclass, I added it to the
superclass.
Update Bishop to support File enum.

I added the appropriate constructor to handle creating and using
File-style positions with the Bishop class. I expanded one of Bishop's
tests.
Update Bishop's tests.

Expanded the tests for the Bishop class and improved their
documentation.
Add move-to-self test for King.
Add more to test and update formatting.

I gave it the checkCompletelyWrongMovement some more movement patterns
to check. I also updated the location of the method beginning brackets,
{, to fit with the rest of the project.
Add movement test.

I implemented a test that walks the right white bishop around the board.
Whitespace change.

Moved the space between methods to one empty line to match the rest of
the project.
Add file/rank constructor to Knight.
Expand Knight init test.
Add more movement tests to Knight.