Extended list of known untuned percussion.

Added the following:

    * crotales
    * hand-held stones
    * scraped slate
    * sponges
    * suspended cymbal
    * tam-tam
    * tubular bells
    * wood planks

It is true that crotales are pitched. The 'untuned percussion' are really
secondary or auxilliary percussion (as opposed to keyboard percussion like
marimba and vibraphone).