refactor: Add common helper method to extract data from response

[lahdjirayhan]

This PR attempts to address #87

To add more detail, the new method is now called in three places:

• get_coordinate_air
• get_city_air
• get_specific_parameter

Also, an important note, that I change _parse_data's return from a list with single dict into just a dict only.

I sincerely expect feedback and improvement.

[Samxx97]

@lahdjirayhan good job on changing the return value of _parse_data method, the method can now be used in wider range of contexts as advertised by it's name, nice work