This would be a very simple castsequence macro. It will cast all spells in that order as long as you keep smashing the button. The reset=target will cause the macro to reset whenever you change your target.
Resets can also be triggered by other conditions like entering/leaving combat or after x seconds. You would just need to replace target with combat or a number. And if i recall correctly the usual modifieres ctrl, alt and shift work too.
I didn't include Serpent Sting because I can't remember if it's possible to tell the macro to skip Serpent Sting if the target is already affected by that debuff so it would be a waste of focus.
well it works exactly like Learza said, its jut that u dont want to use it as "dps macro for mm hunter" cuz ur dps will suck big time. U have to constantly move, etc etc and a lot of other things will **** up ur macro for sure. The only use of that macro in ur direction is to check ur theoretical dps but then again how u will adjust it to affect instant AiS procks?