def link(*from_groups, to_group)
      from_groups.flatten.map do |from_group|
        # Don't add anything we don't already have.
        next if find_link(from_group, to_group)
        link = Link.new(from_group, to_group)
        link.tap { |l| @links << l }
      end.compact
    end
def link(*from_groups, to_group)
      from_groups.flatten.map do |from_group|
        # Don't add anything we don't already have.
        next if find_link(from_group, to_group)
        link = Link.new(from_group, to_group)
        link.tap { |l| @links << l }
      end.compact
    end
Add highlight links to the colorscheme

 @example
   scheme.link(:rubyInstanceVariable, :rubyClassVariable)

 @param [String,Symbol] from_groups
   a list of groups to link from

 @param [String,Symbol] to_groups
   the group to link to

 @return [Array]
   the added links

 @api public