Add validations for options

[antedeguemon]

Hey folks! 🖖

Thanks for the excellent library, httpoison is awesome.

I ran into an issue where all my requests were failing with the checkout_failure error reason. After some debugging, I found that the timeout option I was passing to httpoison was accidentally set to a stringfied integer instead of an integer.

So I had the idea of adding some sort of options validation to HTTPoison. The validation would make the error I had much easier to see since it is not obvious that a string will be interpreted as 0.

I think the easiest approach to implement it would be to use dashbitco/nimble_options.

This would obviously be an enhancement and not a bugfix, but IMO it would be nice to have because it will hopefully save developers time with debugging.