Refactor Move Describable to methodical.interface

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This PR closes #128

I have moved the contents of the file methodical.util.describe to methodical.interface.
I have refactored the occurrences of Describable as well.
And I've deleted the methodical.util.describe namespace.
The diff looks bigger than it is because of my formatter. I couldn't find a formatter in the deps.edn file (so let me know if you want me to reformat it with a specific formatter with a specific config.

camsaul / methodical