Use micromouseonline/mazefiles format for ASCII mazes

[Peque]

Since https://github.com/micromouseonline/mazefiles is likely the most widely used and comprehensive repository of maze files, and the ASCII format defined there has been discussed in depth to (hopefully) become a standard, I suggest updating the generator's (ASCII) output to match that format.

Updating the posts and adding S (start) and G (goal) should be sufficient. 😊