Add response iteration and conversion

[joshsmith]

This PR reworks Stripe response handling to iterate over the response and convert necessary values.

This does not yet handle lists from Stripe nor take in options to push to Stripe.

Reduces scope of certain struct keys as a result.

[coveralls]

Coverage decreased (-0.9%) to 13.75% when pulling 3a0c76a on add-response-iteration-and-conversion into 9600d28 on 2.0.

[DavidAntaramian]

Just FYI, I think coveralls skips over single-line defs for coverage analysis

[DavidAntaramian]

Probably don't want this in released code 💣

[joshsmith]

@DavidAntaramian this is just a code example.

[DavidAntaramian]

Unless what you're saying is that the above renders the below? It might be better to indicate with an

iex> {:ok, resp} = Stripe.Connect.OAuth.token(code)
...> IO.inspect resp
%Stripe.Connect.OAuth.TokenResponse{...}

example

[DavidAntaramian]

I would just specify this as :map

[joshsmith]

The reason I chose :metadata instead of map was to be explicit that it was just structureless data (from Stripe's perspective), and because convert_value has a when is_map(format) clause, which might make that confusing.

[DavidAntaramian]

Gotcha

[coveralls]

Coverage decreased (-0.9%) to 13.75% when pulling 62b2416 on add-response-iteration-and-conversion into 9600d28 on 2.0.

[coveralls]

Coverage decreased (-0.8%) to 13.836% when pulling 21b49b7 on add-response-iteration-and-conversion into 9600d28 on 2.0.

[coveralls]

Coverage decreased (-0.4%) to 14.286% when pulling 84e1986 on add-response-iteration-and-conversion into 9600d28 on 2.0.

[coveralls]

Coverage decreased (-0.4%) to 14.286% when pulling c8ab995 on add-response-iteration-and-conversion into 9600d28 on 2.0.