Arabic Normalizer (c++)  + Buckwalter Romanization Converter

(This pull request is for reviewing)


This will copy the whole map each time this function is called.  If there's just the two systems, you could use a reference:

```
const std::map<unsigned, unsigned> & mapping =
    (romanization_system == 2) ? ISO233_TO_ARABIC : BUCKWALTER_TO_ARABIC;
```

If it's likely other systems would be added, you probably want to make `mapping` a pointer - you have to initialise a reference when you declare it, and you can't change it later, and chaining `?:` to achieve that is going to get ugly fast.