PDOS Plot suggestions

[jolnz]

Hi!

First of all, this is not an issue report, but an improvement suggestion.

I find mcu very useful for quick plots of PDOS obtained from VASP calculations. However, as I had to plot individual or grouped atomic PDOS, I needed to change the code a little bit. You can find the description of these changes below. If you think they would be an improvement for the package, please let me know.

1. I've modified the mcu/vasp/vasprun.py file so the mcu.plot_dos() function can accept atom list as an argument in lm argument, without losing existing functionalities.

Example:

    mcu.plot_dos(lm=['Pt:d','[1]:p','[2,3,4]:s,p'])

    # should plot the DOS of
    #     - the sum of Platinum 'd' orbitals
    #     - the atom with index 1 'p' orbitals
    #     - the sum of atoms with indexes [2,3,4] 's' and 'p' orbitals

2. I also added a new boolean argument in mcu.plot_dos() function called totaldos, which allows to select if TDOS should be plotted (True) or not (False).

Thanks!