update doc to reflect ogg/wav requirement...
update doc to reflect ogg/wav requirement...

Update doc to reflect ogg/wav requirement for native targets, and introduce differences in format handling for native/html5/flash targets.
openfl/openfl,Gama11/openfl,Gama11/openfl,openfl/openfl,Gama11/openfl,NenadBojkovski/openfl,NenadBojkovski/openfl,Gama11/openfl,openfl/openfl