Include local support and add tests

[dieghernan]

Continue #42 and close #41

Thanks @alexwhitedatamine this PR mergs #42 in main with a few modifications:

• I centralized the way the url is built with the new parameter nominatim_server in a single function prepare_api_url().
• I also added tests and improve others, since a side effect of your PR is that now I can check errors on the api calls (by providing a fake nominatim server).
• I added you as contributor in the DESCRIPTION, feel free to modify it.

Cheers

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.32%. Comparing base (9122576) to head (cfa8eed).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #43 +/- ## ========================================== + Coverage 99.29% 99.32% +0.03% ========================================== Files 10 10 Lines 426 447 +21 ========================================== + Hits 423 444 +21 Misses 3 3 ```

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