[sphinx] Fixed warnings

bob/learn/em/gaussian.cpp

bob/learn/em/gmm_machine.cpp

bob/learn/em/isv_base.cpp

bob/learn/em/isv_machine.cpp

bob/learn/em/ivector_machine.cpp

bob/learn/em/jfa_base.cpp

bob/learn/em/jfa_machine.cpp

bob/learn/em/plda_machine.cpp

doc/conf.py

doc/extra-intersphinx.txt

doc/guide.rst