Support generics, forward references and case conversion

[avlonder]

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[avlonder]

On my side, the last benchmark is highlighted in red. Is this a problem?

[mciszczon]

On my side, the last benchmark is highlighted in red. Is this a problem?

Sometimes we might want to trade a small performance hit for highly enhanced functionality, right? But some of the tests still fail, some due to the usage of newer Python functionalities in Python 3.7 and 3.8 environments, some seem to be legit issues with the code.

You can try to run tests on different Python versions locally, and I'll try to also look into it in the upcoming days. Sorry for that, a bit busy right now. But definitely let's push this forward so we can finally merge it into the repo.

@konradhalas What do you think about the change_keys part? I do agree it's a bit out of scope of the project.