Problem: need bitmap class

The matching engine needs a bitmap class. Solution: take the bitmap
class we used in OpenAMQ and port to CZMQ standards. As this is still
experimental, I'm keeping this in Malamute, in src/labs. At a future
date we can move this into CZMQ.
Merge pull request #11 from hintjens/master

Problem: need bitmap class
Added missing include of labs/zbits.h