migrate remaining code to the new maps

examples/word_counter/word_counter.v

@@ -26,10 +26,7 @@ fn main() {
 		m[key] = m[key] + 1// TODO m[key]++
 	}
 	// Sort the keys
-	mut keys := []string
-	for e in m.entries {
-		keys << e.key
-	}
+	mut keys := m.keys() 
 	keys.sort()
 	// Print the map
 	for key in keys {