New primitive: scroll_text_to.

  This allows you to scroll the text to the given line.
  scroll_text_to now accepts a regular expression.
  "/" now searches in text-mode
  More work on the "manual", available via ":help()"
  Updated help some more.

  Almost ready for a new release
  Fixed the missing link to luafaq.org
  Renamed 'scroll_message_to' to be 'jump_message_to'.
  Allow scroll_message_to to work.
  Updated to install the lumail.help file.

  Also rejigged the installation options to be more sane.
  Fixed next/prev message navigation in message-mode.
  Minor comment updates.