AzureCopy (Go version)

This is a reimplementation of the AzureCopy project (github.com/kpfaulkner/azurecopy) in the GO language.
It is primarily to allow cross platform (Linux/MacOS and Windows) versions of it.

I've had numerous requests for Linux versions, so thought I might as well give it a stab.
Currently the plan is:


- Copy to/from Filesystem (done)
- Copy to/from Azure Blob Storage (done)
- Copy to/from S3 (done)
- Add CopyBlob flag for Azure destination (huge bandwidth savings)
- Copy to/from Dropbox
- Copy to/from Onedrive
- Copy to/from Google Storage
- Copy to/from Azure File Storage