feat: add ft_memmove function

memmove:
	if the src pointer is higher than the dst pointer,
	the function copies each caracter backwards.

ft_memmove.c

@@ -0,0 +1,18 @@
+#include "libft.h"
+
+void	*ft_memmove(void *dst, const void *src, size_t len)
+{
+	if (dst <= src)
+	{
+		ft_memcpy(dst, src, len);
+	}
+	else
+	{
+		while (len > 0)
+		{
+			len--;
+			((char *)dst)[len] = ((char *)src)[len];
+		}
+	}
+	return (dst);
+}