Smallchess face (#272)

* smallchess face

* use correct game-state modifying board move function

* make show last work after undo

* use SCL_Game->ply instead of board[ply_byte]

* beep when cpu is done computing a move

* increase engine strength to ply 3

* match ply type and use the local variable where available

* fix warnings

* add doc to smallchess face

* smallchess: fix compile warnings

* smallchess: move smallchesslib.h to movement/lib

movement/movement_faces.h

@@ -122,6 +122,7 @@
 #include "beeps_face.h"
 #include "accel_interrupt_count_face.h"
 #include "metronome_face.h"
+#include "smallchess_face.h"
 // New includes go above this line.
 
 #endif // MOVEMENT_FACES_H_