Improved documentation
Added Slowdown near Goal

Altered control policy to slowdown when close to the goal, to avoid
overshooting.
Broke out state_estimate into a function, because I might want to
experiment with different methods (such as weighted average of
particles).
I still have a problem where the particle cloud and actual location can
diverge. Random injection of particles at high likelihood locations
could help.
Added random particle injection
Random injection for navigating robot
update documentation