Add the GFF file parser
user
```ruby
module Gff
  class Record
    attr_accessor :seqid,
                  :source,
                  :type,
                  :start,
                  :end,
                  :score,
                  :strand,
                  :phase,
                  :attributes

    def self.ncol
      9
    end

    def initialize(options)
      options.each do |key, value|
        send(key.to_s + "=", value)
      end
    end
  end

  class Attribute
    attr_accessor :id,
                  :name,
                  :alias,
                  :parent,
                  :target,
                  :gap,
                  :derives_from,
                  :note,
                  :dbxref,
                  :ontology_term,
                  :is_circular
  end

  def convert_type(value, callback = nil)
    if value == "."
      nil
    else
      if callback.nil?
        value
      else
        value.send(callback)
      end
    end
  end

  def parse(filename)
    File.open filename do |f|
      f.each do |line|
        line.strip!
        next if line.start_with? "#"
        data = line.split "\t"
        if data.length != Record.ncol
          fail "Wrong number of columns (#{data.length} for #{GffRecord.ncol})."
        end

        attribute = Attribute.new
        data.last.split(";").each do |attr|
          key, value = attr.split("=")
          if attribute.respond_to? key.downcase
            attribute.send(key.downcase + "=", value)
          end
        end

        yield Record.new seqid: convert_type(data[0]),
                         source: convert_type(data[1]),
                         type: convert_type(data[2]),
                         start: convert_type(data[3], :to_i),
                         end: convert_type(data[4], :to_i),
                         score: convert_type(data[5], :to_f),
                         strand: convert_type(data[6]),
                         phase: convert_type(data[7], :to_i),
                         attributes: attribute
      end
    end
  end
end
```
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