Support Stream Mode (Issue # 2)

I could not get streaming to work using the [tar-stream](https://github.com/mafintosh/tar-stream) package. I switched it out for the [archiver](https://github.com/ctalkington/node-archiver) package. I hope that is alright. Archiver seems to be more flexible when adding files to the pack.

Added tests to test.js and gulpfile.js as well.