Add client-side command help

This takes steps to provide help for each command to the user. It does this by doing a GET against the command's endpoint on the server then formatting the server's help JSON for output in the CLI.

This handles a wide variety of formats, including:
- `razor command --help`
- `razor command -h`
- `razor --help command`
- `razor -h command`
- `razor command help`
- `razor help command`