720% S3 upload & Assembly speed boost with gos3cmd
- gos3cmd

This replaces aws-cli with the aws go sdk to have much better startup times. I made it so that the cli arguments are the same, so that the calling code nearly does not change.
Before pushing I would like to add some tests for the go code. Just for the sake of it, even though we mainly just pipe arguments into the aws go sdk. But maybe for the metadata handling some tests would be nice.
This is part of a number of performance improvements that we've made since August 2017, all together improving our performance by 720% since then.
