完成 AStar算法

Signed-off-by: ElmerNing <ffxhina@gmail.com>
ruby版本初步完成, 通过文档中3个例子的验证

Signed-off-by: ElmerNing <ffxhina@gmail.com>
完善readme

Signed-off-by: ElmerNing <ffxhina@gmail.com>