Support nested map params (eg. Notification data)

[superchris]

Currently, it appears there is no support for nested maps in Twilio API calls. I first encountered this attempted to call ExTwilio.Notify.Notifications.create with a data property that is a map. It appears that ExTwilio.Api is not able to handle this. It seems possible that changing it to use JSON as the content-type instead of application/x-www-form-urlencoded would solve problems like this. I'd be happy to have a go at doing this, if there is not a reason this is a Bad Idea.

[superchris]

Hmm.. obviously not as simple as that. All the params are capitalized and camel cased. Thanks, Twilio. So gross....