Docstring updates: Fix missing Outcar attributes and update elemental_dos_dos string

[Andrew-S-Rosen]

Summary

• The docs for pymatgen.io.vasp.outputs.Outcar are missing many of the attributes. For instance, it wasn't clear to me until I read the code that the Outcar() object has a total_mag keyword. I've update the docstring to include the missing attributes.

• The docs for pymatgen.electronic_structure.dos.get_element_spd_dos have an incorrect description of the Returns dictionary. This has been updated. Note: There are still some aesthetic issues with the docs, as mentioned in Broken docstrings on the dos module #2292.

[coveralls]

Coverage decreased (-0.6%) to 83.103% when pulling 105253d on arosen93:rosen-docs into 50f5144 on materialsproject:master.

[shyuep]

Thanks.