make FlxSound loop public property
allow using FlxSound if FLX_NO_SOUND_SYSTEM
FlxSound: loop -> looped
FlxSound: stop looping if looped = false while playing
update changelog with FlxSound looped change
Merge pull request #1199 from steverichey/dev

Allow use of FlxSound if FLX_NO_SOUND_SYSTEM, make loop a public property