Problem: Cumbersome to compile z* files in labs folder

Solution: Changed the autotools configuration

Prerequisites: libczmq is installed

Step 1: ./configure --enable-labs=yes
Step 2: make
Step 3: make install

Know you've got a library libczmq_labs installed on your system which
can be used in third party projects.
Merge pull request #713 from sappo/master

Problem: Cumbersome to compile z* files in labs folder