`field` should validate the given options

[marcandre]

Just realized we have some calls to field ..., nil: false (instead of null: false).
I believe this should generate an error.
Let me know if you'd like a PR.
Thanks!

[bamorim]

Hey @marcandre the reason we don't do any warnings in these is because we pass the remaining arguments to Ecto and we didn't wanted to map every possible argument for every possible field.

I'd have to weight the pros and cons of doing that check.