created working cmake build for czmq
missing CZMQ_EXPORT for two unit tests
added msvc support for cmake build
added CZMQ_EXPORT to the gsl source
Moved the CMakeLists.txt work into build-cmake.gsl.

The build-cmake.gsl now contains all the new CMake build smarts,
and has GSL rules to explicitly generate the sources and headers list.
The checked in CMakeLists.txt is now generated from build-cmake.gsl.
Merge pull request #380 from guruofquality/cmake_work

created working cmake build for czmq
Merge branch 'master' of github.com:zeromq/czmq