Notebook updates (#942)

* Added notebook section for DTAgentProgram

* Updated README.md

* Minor

* Added TODO to fix pomdp tests

* Added notebook section on AC3

* Added doctests to agents.py

* Fixed pomdp tests

* Fixed a doctest

* Fixed pomdp test

* Added doctests for rl.py

* Fixed NameError in rl.py doctests

* Fixed NameError in rl.py doctests

* Minor fixes

* Minor fixes

* Fixed ImportErrors

* Fixed all doctests