Throw an error if unexpected keys are provided

[laborg]

I thought I stumbled over this bug #936 but what I actually missed is the initial upper case of Pages in the @contents block.

It would be good to throw an error when unexpected or misspelled keys are provided.

@autodocs only accepts: Modules, Filter, Pages, Private, Public, Order. Example keys that would error: Module, pages, DocTestSetup
@contents should only accept Pages and Depth
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