Ball speed calculation is wonky

[cogwheel]

The ball moves a lot faster diagonally than orthogonally.

The ball_x_delta and ball_y_delta are both set to speed on game start. This means the actual distance covered per frame is sqrt(2) * speed.

When the ball hits a paddle, the ball delta perpendicular to the paddle is set to +/- speed. The ball delta parallel to the paddle is set to a value that only depends on where along the paddle the ball hit.

So after the first hit with the paddle, one component is always equal to speed and the other is unrelated to speed entirely.

This makes the movement erratic and unintuitive. Maybe should be a hard mode?

[cogwheel]

Partially addressed by 507f122

The ball starts out moving at the actual speed instead of sqrt(2) * speed.