Add an examples directory

[ewanharris]

commander and yargs, have an examples directory that shows how to build different CLIs using them. It would be good to have that in cli-kit

I imagine we want something like

• Simple no command CLI
• CLI with commands inline
• CLI with commands separated into files
• CLI setup to consume others as an extension

These could also be used as integration tests. We should make sure they don't get published to npm also