zmqpp: new package

Now that zeromq has been bumped to version 3.2.2, we need to provide the
C++ binding using a separate package.  The zmqpp package provides a
high-level C++ wrapper library around the zeromq C API.

Signed-off-by: Simon Dawson <spdawson@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>