get_captures_by_partition: Get captures within each piece-specific partition
In pmckenz1/boardmakr: boardmakr

Partitions the game based on the number of a specific type of piece remaining on the board, and outputs the captures that occurred during that partition.

1	get_captures_by_partition(game, partitionpiece, capturingpiece = NULL)

`game`	a full game returned by get_boards()
`partitionpiece`	the piece by which the moves in the game should be partitioned
`capturingpiece`	optional, a specific piece that is making captures during each partition