More user friendly hologram CLI

[jlewallen-hc]

The existing hologram CLI script is too opaque for new users. It lacks self-documentation and discoverability.

$ hologram -h
Usage of hologram:
$ hologram
Usage: hologram <cmd>
$ hologram use -h
[ERROR  ] 2021-02-11T00:00:00-00:00 User example is not authorized to assume role arn:aws:iam::012345679:role/-h!

This MR replaces the flag implementation with spf13/cobra which includes features like usage messages and typo correction.

$ hologram
Easy, painless AWS credentials on developer laptops
The hologram CLI is a tool from the https://github.com/AdRoll/hologram application

Usage:
  hologram [command]

Available Commands:
  help        Help about any command
  me          Use your default role
  use         Use a specific role

Flags:
  -h, --help      help for hologram
  -v, --version   version for hologram

Use "hologram [command] --help" for more information about a command.

$ hologram fuse
Error: unknown command "fuse" for "hologram"

Did you mean this?
    use

Run 'hologram --help' for usage.

$ hologram use -h
Usage:
  hologram use <role> [flags]

Flags:
  -h, --help   help for use

$ hologram --version
hologram version 1.2.3

[CLAassistant]

All committers have signed the CLA.