Backup package

We are first going to write the backup package, of which we will become the first customer when we write the associated tools. The package will be responsible for deciding whether directories have changed and need backing up or not, as well as actually performing the backup procedure too.

Obvious interfaces?

The first thing to think about when embarking on a new Go program is whether any interfaces stand out to you. We don't want to over-abstract or waste too much time up front designing something that we know will change as we start to code, but that doesn't mean we shouldn't look for obvious concepts that are worth pulling out. Since our code will archive files, the Archiver interface pops out as a candidate.

Create a new folder inside your GOPATH called backup, and add the following archiver.go code:

package backup

type Archiver interface {
  Archive(src, dest string) error
}

An Archiver interface will specify a method called Archive that takes source and destination paths...