Live coding of Ruby Chess version 4 part 3
* possible_moves castling (00:00)
* inspect (03:47)
* castling_default (04:44)
* queenside castle (06:24)
* allows piece capture (09:47)
* allow knight move (11:18)
* allow queen move (13:02)
* == test for different class (13:34)
* move_str bug with piece not capitalized (14:39)
* cannot castle when in check (15:44)
* cannot castle through check (22:28)
* castles through a clear path (24:45)
* pawn moves (29:15)
* pawn capture (31:30)
* pawn capture en passant (32:30)
* pawn promotion (38:35)
* pawn promotion upon capture (53:24)
