- Used a docker image with a more recent version of Debian
- Enabled colours for gcc and clang
- Updated clang-tidy from 4.0 to 7.0
- Enabled some diagnostic checks for clang-tidy, and disabled others that gave false positives
- Made clang-tidy read system header files, while ignoring their errors

- Fixed clang-tidy version
- Moved CI to separate .sh files