Rewrite the CLI in Go

[hassy]

The current CLI is written in Node.js (to help get a working version out quickly), however, as popular as Node.js is, it's not installed everywhere, and it's especially less likely to be installed on DevOps engineers machines (who would be the ones setting up Llama), which limits its appeal.

Going forward, the CLI should be rewritten in Go:

• A self-contained binary is easier to distribute - as a download or as a deb/rpm package
• There's an official AWS SDK for Go
• There's a number of solid libraries for building CLIs to make the job easier

[hassy]

Not really needed with #16