Updated such that show_text honours colours.

  This matches the (stalled) work that has already been done,
 and allows this to work as expected:

    function x()
       txt = { "${colour:red}Steve",
               "${colour:blue}Kemp",
               "${bold}Has",
               "${underline}Definitely",
               "Made this work" }
       show_text( txt )
       global_mode( "text")
    end

  This updates #175.