readline: put duplicated code in readline_default.c.v

vlib/readline/readline_test.v

@@ -0,0 +1,20 @@
+import readline { Readline }
+
+fn no_lines(s string) string {
+	return s.replace('\n', ' ')
+}
+
+fn test_struct_readline() {
+	// mut rl := Readline{}
+	// eprintln('rl: $rl')
+	// line := rl.read_line('Please, enter your name: ') or { panic(err) }
+	// eprintln('line: $line')
+	mut methods := []string{}
+	$for method in Readline.methods {
+		// eprintln('  method: $method.name | ' + no_lines('$method'))
+		methods << method.name
+	}
+	// eprintln('methods: $methods')
+	assert 'read_line_utf8' in methods
+	assert 'read_line' in methods
+}