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]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

Additional details and impacted files

@@            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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