module GitHub::Markup

def command(command, regexp, &block)
  command = command.to_s
  if !File.exists?(command) && !command.include?('/')
    command = File.dirname(__FILE__) + '/commands/' + command.to_s
  end
  add_markup(regexp) do |content|
    rendered = execute(command, content)
    block ? block.call(rendered) : rendered
  end
end