update vals: make it so that the user doens't have to know what what is in camb or not.

[samueldmcdermott]

rework yam_io.py to be more "active" (ideally: let it return a dictionary but also update the CAMBparams instance)

[samueldmcdermott]

• [x] move update_vals from camb_ps_maker to yam_io
• [x] allow this to update the dictionary and and the CAMBparams instance