Just introduced GoogleTest for TeXmacs and make it work under cmake.
For example:
```
mkdir build && cd build
cmake ..
cmake --build tests -- -j8
ctest -VV
```
Runs all the unit test.
Later, I will introduce travis build for
https://github.com/texmacs/GNUTeXmacs . This is another reason I created the new repo. Feel free to create PR on any texmacs repo, since the patches are downloadable in a PR, hence it is easy to apply the changes to the offical SVN repo.