Eoin add domains script

Added a script to generate the "domains = ..." regex from the IANA maintained file at http://data.iana.org/TLD/tlds-alpha-by-domain.txt. (I didn't add any tests because it's a small script which has to be manually copy/pasted anyways--it's otherwise never actually used in code.)
another idea (probably simpler) would be to use something like:

```python
print(
    '|'.join(
        line.lower() for line in domain_data.read().splitlines()
        if not line.startswith('#') and line.strip()
    )
)
```