function getCssFontsUrl(options) {
  if (options.cssFontsUrl) {
    return options.cssFontsUrl
  } if (options.cssPath) {
    return path.relative(path.dirname(options.cssPath), options.outputDir)
  }

  return './'
}
Based on given options, compute value that should be used as a base URL for font files from the generated CSS

If a `cssFontsUrl` option is explicitally provided, it overrides default behaviour

Else if the CSS was output at a custom filepath, compute a relative path from there

Just return './' otherwise

@param  {Object} options
@return {void}