[book] Some tweaks to fix cubicweb-documentation package generation
- Fix up PYTHONPATH setting to make sure sphinx can find cubicweb modules
- Add a few missing build-dependencies
Latest changes
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* table of `all latest changes`_
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.. _all latest changes: view?rql=Any+M%2CX+WHERE+X+modification_date+M+ORDERBY+M+DESC+LIMIT+30