EDIT main.lisp
add search problem and node ADTs
EDIT grid.lisp
created GenGrid function
EDIT main.lisp
* added general search method
EDIT grid.lisp
* changed operators to return new grid (non distructive)
* changed operators to return cost of operator
EDIT main.lisp
* fixed bugs in general search and expand
EDIT grid.lisp
* added update function to add new block after every move
* added find-max function to find largest block in grid