Fix MDP class and add POMDP subclass and notebook (#781)

* Fixed typos and added inline LaTeX

* Fixed backslash for inline LaTeX

* Fixed more backslashes

* generalised MDP class and created POMDP notebook

* Fixed consistency issues with base MDP class

* Small fix on CustomMDP

* Set default args to pass tests

* Added TableDrivenAgentProgram tests (#777)

* Add tests for TableDrivenAgentProgram

* Add tests for TableDrivenAgentProgram

* Check environment status at every step

* Check environment status at every step of TableDrivenAgentProgram

* Fixing tests

* fixed test_rl

* removed redundant code, fixed a comment