Material Shadow Stylus Mixin

This is a Stylus port of the Google Material Design Shadow Helper

paperShadow(level = 1)
	if level == 1
		box-shadow 0 1px 3px rgba(0,0,0,0.12), 0 1px 2px rgba(0,0,0,0.24)
	else if level == 2
		box-shadow 0 3px 6px rgba(0,0,0,0.16), 0 3px 6px rgba(0,0,0,0.23)
	else if level == 3
		box-shadow 0 10px 20px rgba(0,0,0,0.19), 0 6px 6px rgba(0,0,0,0.23)
	else if level == 4
		box-shadow 0 14px 28px rgba(0,0,0,0.25), 0 10px 10px rgba(0,0,0,0.22)
	else if level == 5
		box-shadow 0 19px 38px rgba(0,0,0,0.30), 0 15px 12px rgba(0,0,0,0.22)