(python-chess, stockfish) Allow the robot to En passant

[nicglazkov]

Is your feature request related to a problem? Please describe.
When the move chosen by stockfish is en passant, the robot is unable to remove the piece captured. There should be a check using is_en_passant as part of python-chess to determine if two moves are needed during the same turn.

Describe the solution you'd like
The robot should be able to move both pieces in the same turn, and en passant correctly.