* Update test_agents.py

pep8 changes, showed flake8 errors

* Update test_agents.py

* Update test_agents.py

* Update test_agents.py

* Update test_text.py

added missing whitespace after comma

* Update utils.py

added space after comma

* Update search.py

added space after comma

* Update probability.py

added space after comma

* Update learning.py

added space after comma

* Update planning.py

added double_tennis_problem

* Update rl.py

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 search.py

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

* Update search.py

* Update search.py

* Update search.py

* Rearranged Tests

- test_ngram_models to the top
- added test_viterbi-segmentation
- removed test_unigram_text_model

* "test_ngram_models" to "test_text_models"

* Add flake8 config file

* Fix flake8 for test files

* Made Log Usage Consistent in text.py

* Added Explicit Imports from utils