Better error message on invalid `@derive Jason.Encoder` options

[LauraBeatris]

Current behavior

When passing an invalid option, eg:

@derive {Jason.Encoder, invalid: [:__meta__]}

It returns the following error: cannot encode metadata from the :__meta__ field for CrosswordsApi.Users.User to JSON.

Expected behavior

Could the error be explicit that expect or only should be passed as valid options only?

[michalmuskala]

Yes, that makes sense. PRs welcome!