Always returns start and end nodes when a path is found in astar
Merge pull request #21 from pierredavidbelanger/fix_empty_result_astar

Always returns start and end nodes when a path is found in astar
it makes sense,  thanks!
fix bugs in astar algorithm
optimize astar algorithm with an extra array for fast testing openset
Merge branch 'develop'
Merge branch 'master' of https://github.com/xtaci/algorithms