Support basename in constructor for /usr/share/hunspell/*.dic dictionaries

Support basename such as strings `en_US` or `nl` in the constructor for dictionaries that are found on Debian/Ubuntu in `/usr/share/hunspell/*.dic`.

This would make the code shorter in use.

Example usage would be

```python
hun_en = HunSpell('en_US')
hun_nl = HunSpell('nl')
```