Changed the Piece and Board classes slightly so that I can make an efficient C++ agent.

I plan to make SilverFish as good as I possibly can.
Rather than writing 6 different mediocre sample agents like I did last year, I will just focus on this one.

Technically I can't enter my own competition, so SilverFish is still just a sample agent.

Anyway it still just defaults to random moves at the moment.

- Fixed C++ agent (yay)
- Added Java agent (ew)
- Renamed some things (why?)

As a result, found an issue where qchess was printing "-1" as the index whenever a King was selected.
I don't know why that didn't break the python agent, but it definitely breaks the C++ agent, so I fixed it.