Refactoring and prep for threaded searching

Made King value higher
Made Piece accessors consistent
Piece is now a 1D array
Some initial work on Promotion, including adding rules to Pawns
Searcher now launches a thread; doesn't terminate correctly though
Many positive changes.

Pieces are now generally const *'s throughout.
Fixed a bug in search that caused searches to fail miserably when white
moved first.
Still todo: get piece promotion through movelists working.
Threads now starting and stopping without barfing.