More built-in waveforms

[olofson]

With #152 done, we could add lots of nice, handy built-in waves without increasing the engine startup time and base memory footprint.

Now that we have off-line rendering via the 'wave' directive as well, the lines are kind of blurred. In addition to actual waves (simple, named objects, always rendered exactly the same), we could provide a library of programs suitable for both live processing and rendering to waves. That is, parametric waves, without any explicit engine support!