add `each_from` method (`each` with lower_bound) in class Prime.

prime_each_from.rb

require 'prime'
class Prime
  def each_from lower_bound = 0, upper_bound = nil
    return to_enum :each_from, lower_bound, upper_bound unless block_given?
    if lower_bound.is_a? Range
      range = lower_bound
      lower_bound = range.first
      upper_bound = range.exclude_end? ? range.last - 1 : range.last
    end
    flg = false
    each upper_bound do |pr|
      yield pr if flg ||= pr >= lower_bound
    end
  end
end