Compress takes a source and variable writers and walks 'source' writing each file found to the tar writer; the purpose for accepting multiple writers is to allow for multiple outputs (for example a file, or md5 hash) Copied with minor modifications from https://medium.com/@skdomino/taring-untaring-files-in-go-6b07cf56bc07.

CompressFolder takes the name of a folder to compress, and the name of a file in which to store it.

Uncompress takes an io reader containing a tar/gz archive and expands it to the specified dst folder, trying to retain file modes.

UncompressFile takes the name of a tar/gz archive file and expands it to the specified dst folder, trying to retain file modes.