Powerful font-importing controls…

Compared against 3.1.0 -
for incremental changes,
see the 3.2 beta changelogs…

• BREAKING: Change $font-path default to '' (empty string)
  so that no path is prepended to fonts without explicit settings.
• 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: We no longer accept regular as a font-variant.
  Use the CSS-friendly normal instead.
• BREAKING/NEW: We now sort font-face src into the proper order for importing,
  based on the fontsquirrel generated syntax.
• BUGFIX: font-family function/mixin return proper font-name
  when given an alias keys.
• NEW: Allow sub-maps for each font variant (in addition to strings),
  optionally containing any or all of the following keys:
  • path: generic path to font-files for the given variant,
    the same as providing a string instead of a map.
  • svgid {string}: the proper fragment ID for svg fonts, as needed.
  • local {list}: list of font-names to include as local() src
    for the given variant.
  • <format> {string}: optionally provide different paths per font-format,
    Base64 font data, or additional formats for importing.
• NEW: Allow either string or number values
  for font-weights (e.g. 200 or '200' ).
• New: Supports unicode-range CSS property in font maps,
  as described on MDN.