Resolved an issue with SQS messages.
Added configurable retries to the InstanceProfileCredentials provider.

You can now supply a number of times to retry failed attempts
to constructor via `:retries`. Failed attempts to reach the
instance metadata service will retry n times with exponential
backoff, starting at 1,2,4, etc seconds.

    # makes at most 4 attempts to load credentials
    InstanceProfileCredentials.new(retries:3)

Based on implementation in the v1 SDK here:
https://github.com/aws/aws-sdk-ruby/pull/634
Added CHANGELOG entry for response stubbing.
More CHANGELOG entries.