Shaper.schelp, Wavetable.schelp: moved wavetable description to Wavetable.schelp

as suggested in <http://new-supercollider-mailing-lists-forums-use-these.2681727.n2.nabble.com/buffer-sine1-td7598249.html#a7598280>
Ndef.schelp: adjusted volumes and fades, corrected document link to 'demonstrations'