SNAKE - Page Scrolling, add WASD controls

[neur0n-7]

While using the up and down arrows keys, the page moves up and down, making the game annoying to play.

Screen.recording.2025-09-12.9.37.45.AM.webm

Proposed fix: add WASD as another optional control scheme. This effectively does two things:

1. Prevents page scrolling
2. Adds more user controls

[neur0n-7]

We changed changeDir() to the below code, so that WASD also works

let changeDir = function(key){
            // test key and switch direction
            switch(key) {
                case 37: // left arrow
                case 65: // 'A'
                    if (snake_dir !== 1) // not right
                        snake_next_dir = 3; // then switch left
                    break;
                case 38: // up arrow
                case 87: // 'W'
                    if (snake_dir !== 2) // not down
                        snake_next_dir = 0; // then switch up
                    break;
                case 39: // right arrow
                case 68: // 'D'
                    if (snake_dir !== 3) // not left
                        snake_next_dir = 1; // then switch right
                    break;
                case 40: // down arrow
                case 83: // 'S'
                    if (snake_dir !== 0) // not up
                        snake_next_dir = 2; // then switch down
                    break;
            }
        }