lib/a_star: renames virtual type E to N

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/a_star: replace some class parameters with virtual types

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/a_star: adds a larger test

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/a_star: minor clean up

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/a_star: use heuristic

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