Fullscreen for cpp
Merge branch 'dev' of https://github.com/HaxeFlixel/flixel into dev

# By sergey-miryanov
# Via sergey-miryanov
* 'dev' of https://github.com/HaxeFlixel/flixel:
  Revert back changes in VarTween, it caused bugs while tweening floats
Cleaning up licensing files.
Removing lower cased license.txt file (changing caps in git is a pin in the butt).
Update README.md

Updating upgrade docs instructions.
Updated haxelib.json
Merge branch 'dev'