Use Min.Io to test S3

[mattBrzezinski]

As part of #99 we've introduced a dependency on a 3rd party GCS Bucket for testing S3 capabilities outside of AWS.

To do this properly we should use Min.IO(or something similar) to remove this dependency and keep everything centralized in this package.

We should install Min.IO on the TravisCI runner, setup and configure it and then update the tests here to use that instead of the 3rd party bucket.

[ExpandingMan]

The min.io HTTP API is fully compatible with the AWS API. The only trick is that you need to change the host name in the URL. You can do this in AWSS3.jl by setting a value for the key :endpoint in the AWSConfig, e.g.

AWSConfig(:endpoint=>"http://localhost:9000")