When Jagex/WOM adds a new metric, the package breaks

[Sharpienero]

Fixed Unknown Enum Handling for Future API Additions

Problem
The package would break when a new metric was added to the Wise Old Man API. This creates an exception that would throw if trying to access a route that contained the new metric.

Solution
Implement an error handler that returns Metric.Unknown in the case where the current version doesn't contain said metric, but still return the data. This was achieved by creating a new class called MetaEnum, that I passed into the metaclass param for BaseEnum. Not sure if this is really the right way to do this, or if you want me to change it, but the test class I created passes. I tried to do it via the discussed _missing_ keyword, but I couldn't figure out why that method was never being called.

class MetaEnum(EnumMeta):
    def __getitem__(cls: MetaEnum, name: str) -> t.Any:
        try:
            return super().__getitem__(name)
        except KeyError:
            print(
                f"{name!r} is not a valid {cls.__name__} variant. "
                "Please report this issue on github at https://github.com/Jonxslays/wom.py/issues/new"
            )
            return cls.Unknown

This fix can be found here: #82