pep8 changes, showed flake8 errors

added missing whitespace after comma

added space after comma

added space after comma

added space after comma

added space after comma

added double_tennis_problem

In the pseudocode figure 21.8, the first 'if' starts with argument 's', which is the previous state, not s1(i.e, the current state).

Update rl.py

the 'uniform_cost_search' in notebook 'search-4e.ipynb' resembles more to the pseudocode in book.

* added documentation, standardised docstring quotes

* made search.py pep8 compatible using flake8

* fixed bug in OnlineDFSAgent

minor error fixes.

created a parameter size in the function leave_one_out(learner, dataset, size=None):

…ode#391)

…ode#394)

* Added testcase for agents.py

* spacing around commas was wrong

* Add Perceptron Section

* Add Perceptron Image

* updated games.ipynb with refactored games.py

* fixed typos in games.ipynb

* move play_game into games class

* display current state before prompting for action

* fixed player swap bug

* display available moves to human players

* make tests pass

Add DecisionTreeLearner, NeuralNetLearner and PerceptronLearner tests