--libxo=excellent,pretty

Added libxo support, enabling such things as:

-# checkrestart --libxo=json,pretty
{
  "__version": "1",
  "checkrestart": {
    "process": [
      {
        "pid": 85250,
        "jid": 0,
        "name": "zsh",
        "updated": "Binary",
        "command": "/usr/local/bin/zsh"
      }
    ]
  }
}