Add functionality to no_error

[kalekje]

I think a only_pre_defs flag for the options would be handy..the way it would work is if a user inputs a key that does not have a default value declared, an error is thrown.

(Will work towards a PR, putting it here so I don't forget).

[kalekje]

Proposal below:

-- If true, only keys that were pre-defined in the defs or defaults tables in opts can be used. If not, an error is thrown.
only_pre_defs = false,

[kalekje]

@Josef-Friedrich I think I might be a bit confused with how the no_error option works. I believe if no_error is false, only keys listed in defs can be used. If this is true, then all I would like to do is add keys from defaults to this criteria.

[Josef Friedrich]

that makes sense to me