Two updates

1. Fixes a spelling mistake in the header notes
2. Adjusted the piece encoding to allow each piece value to index
   an array of bitboards in Board. This will allow for efficient
   access to the bitboard that corresponds with a piece type.
Simplify BoardStatus

There is also no need for the complexity here at the moment (90f048b50c5e885a77ea493d9143893c3eda13b3).