Feature: Replaceable fonts

[hacksalot]

Themes should be able to declare overridable named fonts styles using helpers such as fontFace or fontList:

{{! somefile.css }}
h1 {
  font-family: {{fontFace 'heading1'}};
}
p {
  font-family: {{fontList 'default'}};
}

Styles can be declared in the theme's theme theme.json, with or without fallbacks:

"fonts": {
  "default": ["Helvetica Neue", "Helvetica", "Open Sans", "Calibri"],
  "heading1": "Impact"
}

And overridden by the user at generate time:

hackmyresume build resume.json ---heading1 "Droid Sans"