default to returning a string

[drdelambre]

currently, if a response isn't one of three types, the response handler just returns undefined for the response's data property. The API supports more than those three types, so i defaulted to letting it all roll into string processing if not the first two.

Lemme know if whitelisting the type would be better, i'm indifferent

[hoorayimhelping]

solid, and great description!