No support for IAM roles

[matogertel]

Knox doesn't support IAM roles, which is becoming more and more the de-facto authentication inside AWS instead of keys and secrets. See: Automattic/knox#262
I suggest using the native aws-sdk package instead.

[sktt]

semi done in #15

if i get heads up. i will clean it up.

[nick-fytros]

Any news on that matter?