Refactor and more

See merge request !105

The error was that passing to threads the pointer to a variable that
will be copied then destroyed before the end of the thread is a really
bad idea

- Clean all the generated files and folders, even on failed pipeline
- Add the format checking test at initialization

The src folder seems to be re-init between jobs (at least, created
folders are no longer here), so create build and install folders
elsewhere.

NOTE: Build only with clang, see why