Implemented arrow shooting in Wumpus World. Wumpus Environment is now complete.

Fixed bug where dead agents still get to act (Environment)
Improved Direction class to ease 2D Movements (Direction)
Implemented an easier way to iterate with and without walls (XYEnvironment)
Added is_inbounds() method to check if location is within the width and height. Works within walls also. (XYEnvironment)
Multiple Minor Fixes(agents.py)

WumpusEnvironment

Added image for graph in search.ipynb

implemented fixed_lag_smoothing

Made the output of play_game() a bit more verbose

Fixed problem in logic.py and added more test cases

Fix a few typos in README.md

Implementation of Particle Filtering

Implemented forward-backward function in probability.py

Made code easier to read reverting from 79 charaters per line to 100 

Fixed a bug and added tests for logic.py

Modify index of code in ready.md

Implementation of multivariate linear regression

* 'master' of https://github.com/aimacode/aima-python: