Support STSAssumeRoleSessionCredentialsProvider

[avernonquantify]

Where the user credentials are defined within one account and a cross account role provides the permissions to write to the S3 bucket there is a need to use the STSAssumeRoleSessionCredentialsProvider.

This issue would relate to supporting ~/.aws/credentials.

[dukejansen]

Indeed, just using the same chained provider that AWS Java SDK uses under the covers would be very helpful here.

[lareeth]

This pull request #33 fixes this issue, however we need Jeff to accept

CC @jcaddel @jeffcaddel

[avernonquantify]

Any update?

[avernonquantify]

Nearly a year later... Any update?