lib/bucketed_game: make the GameEvent an interface

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/a_star: use asserts in module documentation

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/a_star: adds doc to Link class

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
tests: correct extension of test_a_star expected result

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