Implementation of the A star pathfinding algorithm with a Pygame interface.

The code is runned as follows:

• After running the main file 'A_star_pygame' a window of Pygame appears full of white squares. Every white square is an available free position.
• A first left click in any square sets up the initial position, a second left click in any other square sets up the final point.
• Any other left click in the rest of the board will set up the squares with obstacles.
• At any moment any right click in an already clicked square will set it up again in white color.
• By pressing the space bar the programm starts. The evolution of the process can be seen on the screen. Once it ends, the path is colored in purple.
• To set up a new board, the window must be closed and the main file 'A_star_pygame' must be runned again.

• Implement better aesthetics in the Pygame interface.
• Implement the possibility of setting up a new board directly by pressing space bar again, instead of having to close the window and run again the main file.