Support for body and footer sections like in cc spec

[atufkas]

To be inline with the conventional commit specification we'll need support for real body and footer sections of a log entry.

The JSON might be extended like that:

    {
      "date": "2018-05-08",
      "type": "upd",
      "scope": "ci",
      "desc": "Changed Travis CI install workflow to 'composer update' (instead of install).",
      "body": ["Note: Travis CI is configured to run composer update.", "Cheers, your dev-team."]
      "footer": "fixes #1, #4.",
      "audience": "*"
    },

The value of the body attribute might either be a single string or an array, where elements of arrays mark a single paragraph within the body.