doccument -> document

In hindsight, the variable name "doc" implies we are manipulating the
document itself when, in reality, we are manipulating the index of the
document. "docid" better expresses this concept.

Added self to argument

This change is for consistency.

Cast was not needed since the return value was already being cast. Query
function changed to use heapq.nlargest() for simplicity

Apparently, set() does not equal {}

Problems fixed:
Replaced cmp: 1 instance in line 323 of search.py
Convert set() to {}: 3 instances in line 29 of MDP.py, line 181 and 215
of search.py
Convert .sort() to sorted(): 1 instance in line 150 of text.py
Cast map to list: 1 instance in line 47 of grid.py

Fix a minor error to arguments of flake8 in Travis configuration file

Moved Tests for MDP into Test File

Add tests for the Wumpus World

Implemented Passive Temporal Difference Agent

Fixed ussue where an agent's location set to 0 returned None

Modifications in csp.py and added unit tests in test_cp.py

Added image for graph in search.ipynb