URL compatibility with httpx

[snowman2]

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https://github.com/DavidMuller/aws-requests-auth/blob/2e1dd0f37e3815c417c3b0630215a77aab5af617/aws_requests_auth/aws_auth.py#L195

https://www.python-httpx.org/compatibility/#request-urls

Accessing response.url will return a URL instance, rather than a string. Use str(response.url) if you need a string instance.

[snowman2]

Related: #50

[pk5ls20]

Based on the ideas from this repository and referencing the official documentation, I have completely rewritten a version for httpx authentication. The code is available here: https://gist.github.com/pk5ls20/3081ac14286842da31fdf187bbd5ffef