Allow to set "text" option for specific font family

[tobiasdiez]

The text option is a nice optimization e.g. if you use the font only in a logo. However, most of the time, this applies only to one particular font family, while other families might be used e.g. in the body. Thus it would be nice if "text" could be specified for a certain font family:

families: {
      'Cabin+Sketch': { weight: [300], text: "NUXT!" },
      'Open+Sans': [300, 400, 600],
    },