Enhance Makefile with clean and deptry targets

[tschm]

Added clean and deptry targets to the Makefile. Add also the book target.

Try "make book" and watch out for the _book and _tests folders The "make book" can also be triggered during ci/cd and it is possible to upload the book as webpage. Currently the book only features test and coverage reports. We can also include notebooks and documentation...

[fkiraly]

I get clean and deptry, but what does book do? Would appreciate an explanation.

[tschm]

Book is constructing a static webpage collecting test reports, test coverage etc.

[tschm]

An example for a book is given here https://tschm.github.io/pyhrp/.

[fkiraly]

does this mean, you are suggesting to migrate the documentation from readthedocs to book?