def parse(config)
      hash = {}
      config.each do |label, spec|
        field = Field.new(label, spec)
        hash[field.name.to_sym] = field
      end
      hash
    end
def parse(config)
      hash = {}
      config.each do |label, spec|
        field = Field.new(label, spec)
        hash[field.name.to_sym] = field
      end
      hash
    end
Parses the field configuration as described in {Field}.

 @param [{String => String}] config the field label => spec hash
 @return [{Symbol} => Field] the symbol => Field hash