def add(name, value)
      name = normalize_header name.to_s
      Array(value).each { |v| @pile << [name, validate_value(v)] }
    end
def add(name, value)
      name = normalize_header name.to_s
      Array(value).each { |v| @pile << [name, validate_value(v)] }
    end
Appends header.

 @param [#to_s] name header name
 @param [Array<#to_s>, #to_s] value header value(s) to be appended
 @return [void]