dl: add a complete tested shared library generation/usage example

vlib/dl/example/library.v

@@ -0,0 +1,10 @@
+module library
+
+[export: 'add_1']
+pub fn add_1(x int, y int) int {
+	return my_private_function(x + y)
+}
+
+fn my_private_function(x int) int {
+	return 1 + x
+}