* Implement Topological Sort

- Implemented topological_sort
- Added auxiliary function build_topological
- Updated call to topological_sort

* Use defaultdict to build visited

* Added test

* Update csp.py

Skip first item of iteration

* Update some comments

* Cleanup and remove some duplicate initialization

* Fix some comments quotation and little bugs: raising Exception instead of raising Failure, random.randrange(a,b) instead of random(a, b)

* Fix some comments quotation and remove explicit inheritance from object

* Fix 'r' in front of the ```parse_csv``` comments

* Fix quotation in comments

* Fix quotation in comments and fix bug in 'KB_AgentProgram'

* Modern string formatting in csp.py.

* Modern string formatting in games.py.

* Modern string formatting in learning.py.

* Modern string formatting in nlp.py.

* Modern string formatting in probability.py.

* Modern string formatting in search.py.

* Replaced {0\!r} by {} if %s.

* Corrected a typo.

Style: delete excess parentheses. In some of these cases you need to read ahead to see that the paren is not introducing a tuple, for example.

* Replaced mean with standard lib function introduced in 3.4

* #TODO Replaced every with all

* Proper names for variables introduced in 2to3 conversion.

* modifies Fig. to Figure all over the repository

* fixed a small type in logic.py

* Made Log Usage Consistent in text.py

* Added Explicit Imports from utils

Remove count_if, find_if, every, some, Struct; replace them with modern
Python equivalents.

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

Used tool 2to3 to finish the porting to Python 3 plus some fixes by
hand.

These functions, which I had to implement in Python 2.2, are now
available in standard Python.