Update dos

[ahxbcn]

1. Argument of abacus_dos_run are updated.

• Removed the confusing argument dos_scale and unused keyword dos_nche.
• Revised dos_emin_ev and dos_emax_ev are changed from raw output value (unshifted, not convienient) to range used in real plot.

2. A new mode named atom is added to output PDOS of selected atoms given by argument pdos_atom_indices, which is a list of atom indices started from 1.
3. DOS and PDOS data are now written directly to files, enabling users to easily generate custom plots. All PDOS data are automatically shifted relative to the Fermi energy. dos_emin_ev and dos_emax_ev doesn't restrict the range of outputed PDOS.

• If the mode is atom, will output orbital-resolved PDOS for each atom to PDOS_{species}{atom_index}.dat.
• If the mode is species, total PDOS summed over all atoms of each chemical species is written to PDOS.dat.
• If the mode is species+shell, will output PDOS for each angular-momentum shell (e.g., s, p, d) of each species to PDOS_{species}.dat.
• If the mode is species+orbital, will output PDOS for each orbital (e.g. px, py, pz) of each species to PDOS_{species}.dat.