Use point struct as position

[didiermichel]

This PR intend is to improve code readability.
I introduce Point type that handle x and y value for an element (snake body, apple)

I hope it does bring more readability to the code.

[didiermichel]

Note: code compiles, but I still need to flash and validate everything is still fine.

[deadprogram]

Wouldn't it be better to use image.Point for this? https://pkg.go.dev/image#Point

[conejoninja]

At the time I wrote the original code (many years ago 🤣 ), image.Point was causing some compilation errors, that should have been fixed by now, but, image.Point uses int instead of int16 (used by the display coords), casting will be needed in many places and in my opinion it will make readability worse. I vote for maintaining custom Point Struct instead of image.Point.

[didiermichel]

I cannot say I had thought this through as I didn't know about image.Point 😆

[doniacld]

For history of this structure, it could be nice to have a comment explaining why we are not using image.Point using the comment from @conejoninja.

Suggested change

	type Point struct {
	// Point is a custom type defining a point with x, y coordinates as int16 like the display coordinates.
	type Point struct {

[didiermichel]

I will add the comment.