cxxpiper update

[Derek Davies]

I think cxxpiper is feature complete for a review.  I'm not
completely happy with capitalization and punctuation, but rate, pitch
and volume adjustment are working and it feels fast and responsive to
me.  I introduced a dependency on rubberband, but I'm not wedded to that
library.  It would be good to find somehting that would be appropriate
for other OMs too.  Rubberband does rate, pitch and volume, but doesn't
do pitch range, maybe there's something better?

Should I submit a PR on github?  I'm happy to make a tarball available,
to get it out for review faster, but whatever is best.

Thanks!
Derek