FlxObject.onScreen() -> isOnScreen(), FlxSprite.simpleRenderSprite() -> isSimpleRender()

also made isSimpleRender() public
Update CHANGELOG.md
SfxFader: Fix setting duration in new() and crossFade()
Merge pull request #840 from Gama11/boolReturn

FlxObject.onScreen() -> isOnScreen(), FlxSprite.simpleRenderSprite() -> isSimpleRender()