Option to save/write screen image to disk

[drum445]

It would be useful to have a way to save the screen after Draw() has been ran to a file on disk. Similar to raylib's screenshot functionality.

If there is already a way to achieve this, please let me know

Thanks

[hajimehoshi]

1. Use EBITENGINE_SCREENSHOT_KEY environment variable.
2. You can save an *ebiten.Image by passing this to png.Encode or something, as this implements image.Image.

[drum445]

That's great, thanks @hajimehoshi 👍