Add support for compressing objects

[chdsbd]

Objects could be compressed locally using gzip and then the Content-Encoding header could be set so the file is served correctly.

related: #42

[nick-benoit14]

@chdsbd I think that would be a great addition to the project. I don't currently have the time to implement that, but I would very happily accept a PR though. Thanks for bringing this up, I think this would be a really cool feature. One of the use cases for this tool is deploying very large numbers of files to s3. Other tool's I have looked out break on account of opening too many file pointers. So adding compression seems like a natural next step to support that use case.