Create ENum class

[JSAbrahams]

Description of the feature

There should be a Python ENum class in the standard library of the language, as this is one of the features of the language.

Description of potential solution

Always add an ENum class to the output when creating Python source files (see #17). The standard library could be outputted in its entirety to the output.

Alternatives considered

Perhaps in future, it might be better to have the allow developers to add the standard library of Mamba as a dependency to a project. Note Python has an excellent standard library, so ideally this standard library shouldn't have to add much as Python itself already contains much functionality.

Additional context

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[JSAbrahams]

No longer necessary after #69.