Converts build to duo

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Adds components for duo

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Uses then/promise over chrissrogers/promise

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Splits open and relay into separate modules

To step away from the mixin model

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Updates tests for duo

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Merge pull request #154 from recurly/use-duo

Use duo