Appends the ln first bytes of ns to self

Property definitions

core $ Bytes :: append_ns
	# Appends the `ln` first bytes of `ns` to self
	fun append_ns(ns: CString, ln: Int) do
		if persisted then regen
		var nlen = length + ln
		if nlen > capacity then enlarge(nlen)
		ns.copy_to(items, ln, 0, length)
		length += ln
	end
lib/core/bytes.nit:577,2--584,4