183 fullscreen support

[micheldebree]

Draft for fixing #183

Hardcoded fullscreen

An extra clearing of the screen is done in viewport:End() to eliminate noise in the 'letterboxed' areas. This seems like a hack; I would like to understand why crap is rendered there in the first place.

TODO:

• [x] Fullscreen toggle with keyboard shortcut
• [x] Config setting for starting fullscreen
• [ ] Fix overlay, or disable in fullscreen mode
• [x] Fix mouse support
• [x] Find out why noise is rendered and maybe eliminate that
• [ ] Upgrade SDL2 version for Windows to 2.0.18 or higher

[micheldebree]

This isn't really a hack, since you're clearing the screen buffer before presenting the render buffer. I wonder if it needs to be done every frame though.

The noise looked like it changed on every frame (very quickly anyway). You can have a look if you take out the clearing step.

[micheldebree]

Mouse is not working properly at all in fullscreen :)

[micheldebree]

Mouse is not working properly at all in fullscreen :)

Fixed, but solution needs an SDL2 upgrade