* fixed typos

* fixed several typos

* Corrected test_compare_agents() function

TrivialVacuumEnvironment was missing a pair of parenthesis while creating the "environment" object of the TrivialVacuumEnvironment class
ModelBasedVacuumAgent and ReflexVacuumAgent were also missing parenthesis while creating the "agents" object.

* Reverted changes made to test_compare_agents()

* fixed typo

* Update text.ipynb

* fixing dollar signs

* spacing in text.py

* information retrieval notebook section

* Update text.py

* Update test_text.py

* Update text.ipynb

* 'sentences' to 'samples'

* unigram char model + rename text to word models

* Update test_text.py

* Update text.ipynb

* remove duplicate assert

* DataFile Update

* Update learning.py

* Update search.py

* Update test_learning.py

* Update test_text.py

* Add files via upload

* Update text.ipynb

* Update search-4e.ipynb

* Create CONTRIBUTING.md

* Added ShiftDecoder to notebook

* replaced code with psource

* fix spelling mistakes

* Update text.ipynb

* Update text.ipynb

- Fix relative imports in base of is a package or not
- Fix not working notebooks
- Add notebooks to packages sources