evolve: move status msg to verbose mode in content-divergence resolution
As suggested by Pierre-Yves, lets move these too verbose message for the user
to verbose mode to decrease some noise.
debian: Override default value for SPHINXBUILD in docs/makefile
Sphinx now defaults to Python 3 in Debian Buster, so we need to
explicitly select the Python 2 version of sphinx-build for building
docs.