Currently cppzmq as relatively simple and header only library depends on rather
complex unit test framework googletest.
Current issues:
- Googletest requires downloading and building it every time on travis
as cache support is limited there
- Googletest build is signifficant with comparison to cppzmq unittests
total runtime
Solution: Port existing tests to Catch - header only C++ framework and
gain ~20% build speed up on travis.
Why Catch?
It is well know C++ header only testing framework. It works well, it is
being kept up to date and maintainers seem to pay attention to
community's comments and issues.
We can not use Catch2 currently as we still support pre-C++11 compilers.
It seems that there is a bug in libzmq 4.2.0 cmake configs that prevents
linking to it without installing.
Solution: disable libzmq 4.2.0 for cmake builds
