Add a make coverage target to merge all other coverages, and upload to codecov

Do not remove the .info generated by lcov

Fix the indent in the coverage.cmake file

[skip-ci]

Remove build/* from the coverage, because that code isn’t part of biboumi

Mark some more cmake variables as advanced

Make lcov gcov etc optional

make coverage will display an error instead

Add code coverage support

make coverage runs the test_suite and generates a report