Support for `.aws/config`?

[vspinu]

Please specify whether your issue is about:

• [ ] a possible bug
• [ ] a question about package functionality
• [x] a suggested code or documentation change, improvement to the code, or feature request

My .aws/config file has entries like this

[profile power]
role_arn = arn:aws:iam::1234567891011:role/PowerUserRole
source_profile = default
region = eu-central-1

Which specifies both region and role. This works with aws cli and, surely, there is a common expectation that it should work here as well. Currently .aws/config seems to be ignored (related #18, cloudyr/aws.s3#168).

Would be great if,

1. profiles where searched in .aws./config first for region and role
2. Any roles be assumed automatically like in aws cli