Incremental attack tables

[87flowers]

Step 2 in the 4 step plan: Incremental updates.

• UCI changes:
  • Implements position
  • Adds fen (prints fen).
  • Adds attacks (prints attack tables).
  • Adds perft (splitperft to specified depth from current position).
• Position::move changes:
  • Incremental attack table updates
• Place changes:
  • Change to a more AVX2-compatible format.

[TheRealGioviok]

maybe optimization