Added region support 

### Add supportRegion to enabled region support, default is false.
```
i18n.configure({
    locales:['en', 'zh-tw', 'de'],
    defaultLocale: 'en',
    supportRegion: true,
    directory: __dirname + '/locales',
});
```

Now support zh-tw to map zh-tw.json, generate both zh-tw and zh

```
accepted languages: ['en-us']
return en

accepted languages: ['en-gb']
return en

accepted languages: ['zh-cn', 'en']
return zh

accepted languages: ['zh-tw', 'zh']
return zh-tw
```