lib/a_star: find alternative targets on path

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/bucketed_game: support cancel actions

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/ai: fix typo in doc

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>