* Update treap.py
check merge()
* Update treap.py
random() is used. its difficult to write doctests
l->left
r->right
key->value
add __repr__ and __str__ in preorder
* Added print function into matrix_multiplication_addition.py and removed blank space in data_structures/binary tree directory
* Removed .vs/ folder per #893
* Rename matrix_multiplication_addition.py to matrix_operation.py