Updated the clear primitive to call CScreen::clear_main.

  CScreen now has clear_main to clear the whole window, except
 the status area, and clear_status to clear just the last line.

  This is part of issue #55.
  Updated to use clear_main() not `clear`.

  This prevents flicker and avoids over-writing our message-area.

  This fixes #55.
  New release
  Updated the keybindings section.  Also changed case on
 "lua".