Improve author link flexibility

[mmistakes]

Deprecate existing "hard-coded" author link Liquid spaghetti with something more flexible... similar to how footer links are defined in So Simple theme.

author:
  links:
    - label: "Email"
      icon: "fas fa-fw fa-envelope-square"
      url: mailto:your.name@email.com
    - label: "Website"
      icon: "fas fa-fw fa-link"
      url: "https://your-website.com"
    - label: "Twitter"
      icon: "fab fa-fw fa-twitter-square"
      url: "https://twitter.com/username"
    - label: "Facebook"
      icon: "fab fa-fw fa-facebook-square"
      url: "https://facebook.com/username"
    - label: "GitHub"
      icon: "fab fa-fw fa-github"
      url: "https://github.com/username"
    - label: "Instagram"
      icon: "fab fa-fw fa-instagram"
      url: "https://instagram.com/username"

This would allow users to define what links they'd like, what they link to, their order, and use any of the icons available with Font Awesome.