[REQUEST] Enable support for .air format parameter "Loopstart" in FIght.def/system.def

[PotofWeed]

In Mugen stage.def files, there is a "Loopstart" Parameter which enables animation actions to loop after a certain frame.
Example:

[Begin action 100]
601,0,0,0,60
601,1,0,0,2
601,2,0,0,2
601,3,0,0,2
601,4,0,0,2
601,5,0,0,2
601,6,0,0,2
601,7,0,0,2
601,8,0,0,2
601,9,0,0,2
loopstart
601,10,0,0,2
601,11,0,0,2
601,12,0,0,2
601,13,0,0,2
601,14,0,0,2
601,15,0,0,2
601,16,0,0,2
601,17,0,0,2
601,18,0,0,2
601,19,0,0,2
601,20,0,0,2

however the parameter is only supported inside Stage.def files and not system.def or fight.def files.
Adding this function would allow for more flexibility to create more complex and dynamic screenpack and lifebar designs