Local test coverage of GDL using gcov lcov

OK, we do use the service offered by Codecov but you can compute locally the estimation of test coverage of GDL by the files in the testsuite/ using gcov and lcov. Thanks to @Saynkas for this very promising feedback.

cmake .. -DCMAKE_INSTALL_PREFIX=$PWD \
-DCMAKE_CXX_FLAGS:STRING="-fprofile-arcs -ftest-coverage" \
-DCMAKE_C_FLAGS:STRING="-fprofile-arcs -ftest-coverage"
make -j 4 install
lcov  --capture --initial --directory . --output-file coverage1.info
make -k test
lcov --capture --directory . --output-file coverage2.info
lcov --add-tracefile ./coverage1.info --add-tracefile ./coverage2.info --output-file coveragefused.info
lcov --remove coveragefused.info "/usr*" "CMakeFiles/3.16.3/*" -o coveragefused.info
genhtml coveragefused.info --output-directory out
firefox out/index.html &

We clearly have to extend the tests to improve the coverage of the c/c++ code !