def each_header   #:yield: +key+, +value+
    block_given? or return enum_for(__method__)
    @header.each do |k,va|
      yield k, va.join(', ')
    end
  end
Iterates through the header names and values, passing in the name
and value to the code block supplied.

Example:

response.header.each_header {|key,value| puts "#{key} = #{value}" }