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.

* fixes an error in search.py

* modifies the method name 'exec' which is a built-in name

* modifies Fig. to Figure all over the repository

* fixed a small type in logic.py

* Change variable names from s_prime to s1, current_state to s1

* Sane default for update_state

* removes obsolete Fig dictionary from utils.py

* modified rl notebook according to the new Figure conventions

* removes 'import Fig' and changed the names of Figures

* fixes a small error (by me) in executing the cells in rl notebook

* Made Log Usage Consistent in text.py

* Added Explicit Imports from utils

* changes a typo of file name to /aima-data

* modified some documentaion and removed doc tests

* changed the names like Fig[2, 3] and added unit tests for search.py

* adds Fig[4.23] graph which is 1-dim state space problem

* adds LRTA star agent class

* adds fully implemented LRTA star agent

* adds tests for LRTA star agent

Apparently, set() does not equal {}

Problems fixed:
Replaced cmp: 1 instance in line 323 of search.py
Convert set() to {}: 3 instances in line 29 of MDP.py, line 181 and 215
of search.py
Convert .sort() to sorted(): 1 instance in line 150 of text.py
Cast map to list: 1 instance in line 47 of grid.py

- 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.

use “raise NotImplementedError” for abstract methods

Remove astar row from compare_graph_searchers table because it's sensitive to trivial changes. Needs real tests instead.

 * graph_search missed deduping nodes in the frontier
 * astar_search didn't use 3rd-edition pseudocode
 * InstrumentedProblem didn't forward the path_cost method,
   so all the doctest results on instrumented cost-sensitive
   problems were wrong

Also filled in breadth_first_search and per-node memoization 
of h (to fulfill the doc comment saying that was done).

There's a remaining problem that sometimes trivial refactorings
change the amount of search that is done, slightly, which should
not happen since the code is supposed to be deterministic.