* Fix Python code
* Add the pythontutor blocks of the chapter tree, heap, graph, searching, sorting, divide and conquer, dynamic programming and greedy.
Improve the pythontutor blocks of the chapter array and linkedlist and backtracking.
Add the tutorial of pythontutor in how-to-read section.
* Reduce the image's file size.
* Update copyright
* Update the Python code
* Fix the code comments in ArrayBinaryTree
* Fix the code comments in ArrayBinaryTree
* Roll back time_comlexity.py
* Add the visualizing code(pythontutor) blocks to the chapter complexity, data structure, array and linked list, stack and queue, hash table, and backtracking
* Fix the code comments
