strip indentation for Ruby heredoc

dedent

# strip indentation
class String
  def dedent
    margin = self.scan(/^ +/).map(&:size).min
    self.gsub(/^ {#{margin}}/, '')
  end
end


def usage
  puts <<-EOS.dedent
    Overview:
      foo bar baz

    Usage:
      foo <spam> <ham> <eggs...>

  EOS
  exit
end