vlib: add a clipboard module (Windows, macOS, X)

vlib/clipboard/clipboard_test.v

@@ -0,0 +1,23 @@
+import clipboard
+
+fn run_test(is_primary bool){
+	mut cb := if is_primary {clipboard.new_primary()}else{clipboard.new()}
+	if !cb.is_available() {return}
+	assert cb.check_ownership() == false
+	assert cb.copy("I am a good boy!") == true
+	assert cb.check_ownership() == true
+	assert cb.paste() == "I am a good boy!"
+	cb.clear_all()
+	assert cb.paste().len <= 0
+	cb.destroy()
+}
+
+fn test_primary(){
+	$if linux {
+		run_test(true)
+	}
+}
+
+fn test_clipboard(){
+	run_test(false)
+}