title: display help if incorrect or mission option in click
body: <p>When I put invalid arguments to a command, only this is displayed:</p>
  
  <pre><code>Usage: ugen.py [OPTIONS]
  
  Error: Missing option "-o" / "--out_file".
  </code></pre>
  
  <p>I would like to display the whole help message as with <strong>--help</strong> option</p>
  
  <p>My decorated function:</p>
  
  <pre><code>@click.command(name="ugen")
  @click.help_option("-h", "--help")
  @click.option(
      "-o", "--out_file",
      help="Output file where data is written.",
      required=True
  )
  @click.option(
      "-i", "--in_file", multiple=True,
      help=(
          "Input file/s from which data is read. "
          "Can be provided multiple times. "
          "Although always with specifier -i/--in_file."
      ),
      required=True
  )
  def main(out_file, in_file):
      code here
  </code></pre>