Code live lock when no path is found

[AfroDisco]

Added a simple boolean variable to track the state of the algorithm and return something empty when no path is found.
Added and fixed (partially) the documentation

[coveralls]

Pull Request Test Coverage Report for Build 848

• 2 of 4 (50.0%) changed or added relevant lines in 1 file are covered.
• 4 unchanged lines in 4 files lost coverage.
• Overall coverage increased (+0.6%) to 90.671%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
PathPlanning/ProbabilisticRoadMap/probabilistic_road_map.py	2	4	50.0%

Files with Coverage Reduction	New Missed Lines	%
PathPlanning/LQRRRTStar/lqr_rrt_star.py	1	76.09%
PathPlanning/RRT/simple_rrt.py	1	91.67%
PathPlanning/ProbabilisticRoadMap/probabilistic_road_map.py	1	87.5%
PathPlanning/ClosedLoopRRTStar/closed_loop_rrt_star_car.py	1	81.1%

Totals
Change from base Build 847:	0.6%
Covered Lines:	6619
Relevant Lines:	7300

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💛 - Coveralls

[AtsushiSakai]

@AfroDisco Thank you for your PR!!