More control over font-variants

3.2.0-beta.2 - 01/23/18

• BREAKING: Move svgid and local into font-variant sub-maps,
  since the required names are variant-specific.
• BREAKING: Remove $font-formats global,
  in favor of formats key inside font-maps.
  • font-face() mixin no longer has $formats parameter.
  • import-webfonts() mixin no longer has $formats parameter.
• BREAKING: Change $font-path default to '' (empty string)
  so that no path is prepended to fonts without explicit settings.
• BUGFIX: font-family function/mixin return proper font-name
  when given alias keys.
• INTERNAL: Re-structure internal logic to normalize font maps,
  and handle additional font options.