Thorough comparison between CLASS and CAMB

[adematti]

Tests are implemented to check for potential bugs in cosmoprimo wrapping, e.g. https://github.com/adematti/cosmoprimo/blob/b1b60c6e8423d5b00156671531874fe750600a15/cosmoprimo/tests/test_cosmology.py#L164
but it'd be good to perform more thorough checks, playing with CLASS/CAMB precision parameters, etc.,
and make a note of it.