* Update search.py

Commenting issues fixed (spacing and punctuation was off sometimes).

* Update agents.py

* Update canvas.py

Grammar

* Update grid.py

* Update learning.py

Added period

* Update logic.py

Fix quoting

* Update mdp.py

Fixed quoting

* Update nlp.py

Capitalization and punctuation fixes

* Update planning.py

* Update probability.py

* Update rl.py

'th' to 'the'

* Update search.py

* Update text.py

* Update utils.py

* Update utils.py

* Update utils.py

* Update learning.py

Typo

* Update utils.py

* Added implementation of the cake problem

* Added test for three_block_tower and fixed a bug in three_block_tower code

In the precondition positive list, I am not sure whether b!=x is the best way to represent the condition. IsNot(b, x) can be used instead.

* Minor docstring changes

* Added Spare Tire Problem

* Fixed a bug in substitute method of class Action

* Fixed minor typo in comment

* Added Action class for PDDL

* Added tests for Action class

* Changed doc string

* Added PDLL class

* Added Air-Cargo-problem

* Tested Air Cargo Problem

* Made Log Usage Consistent in text.py

* Added Explicit Imports from utils

Used tool 2to3 to finish the porting to Python 3 plus some fixes by
hand.