Show less of the irrelevant files, and use the correct link in the README file

- Improved the overall look of the page
- Coverage generation using lcov and gcov
- Using less gitlab server page by removing interjob artifact generation

Thanks @thodkatz for the suggestion!

- Enabled @internal functions
- Excluded `lib` directory with external libraries
- Enabled call graphs for functions
- Enabled SVG so that graphs are interactive
- Enabled showing even undocumented entities