Modify get params to use api_key defined in params

[harshulsahni]

the _get_params function only relied on tmdb.API_KEY = ... to set an API key. This PR aims to add functionality so that the user can specify an API key in every function to eliminate this global dependency.

See the test test_tmdb_get_params_no_api_with_search in test_base.py for example usage.

Also, this PR simplifies some boolean and string logic to for conciseness.

[harshulsahni]

everytime I change the API_KEY to None, I "reset" it like so to preserve the other tests

[celiao]

@harshulsahni Why do you want to use more than one API Key?

[harshulsahni]

@celiao I don't want to use more than one API key, but rather I would like the endpoint functions (e.g. search.movie()) to be used without having to define the API key at the top of some file. It would be much cleaner (in my opinion) to have the API key defined in the arguments of these functions so they can be more modular.

[celiao]

Thank you @harshulsahni for the contribution and the thoughtful implementation! The code itself is clean and the tests are thorough.

After consideration, we're going to keep authentication simple — the global tmdb.API_KEY = 'your_key' pattern is intentional and central to the tmdbsimple philosophy. Adding a second way to authenticate risks confusing users (particularly students, who are a part of our audience) about which approach to use.

For the rare multi-tenant use case, users can always save and restore the global key around their calls. Closing for now, but genuinely appreciate your suggestion and PR!