* Added Action class for PDDL

* Added tests for Action class

* Changed doc string

* Added PDLL class

* Added Air-Cargo-problem

* Tested Air Cargo Problem

* Intro and representation of MDPs in code

* Added Image for MDP

Style: delete excess parentheses. In some of these cases you need to read ahead to see that the paren is not introducing a tuple, for example.

* Replaced mean with standard lib function introduced in 3.4

* #TODO Replaced every with all

* Proper names for variables introduced in 2to3 conversion.

* fixes an error in search.py

* modifies the method name 'exec' which is a built-in name

* adds table for Figures of implemented data structures

* fixed a small typo

* modifies Fig. to Figure all over the repository

* fixed a small type in logic.py

* Change variable names from s_prime to s1, current_state to s1

* Sane default for update_state

Following a suggestion by C.G.Vedant, changed |implies| to |’==>’|