Allow to give location hints.

This refs #3 and I am pretty sure this will please both sides.
Hints can be given via YAML's key/value syntax in the city list, all
Other values will be parsed as a string, like before. E.g.:

```yaml
cities:
  - "Livingstone"                           # "Livingstone"
  - {"Livingstone" : "Livingstone, Zambia"} # "Livingstone, Zambia"
```