Add options to determine whether to output d.out

[hityingph]

For very complex system containing several hundered atoms in primitive cell， when using compute_phonon, the size of D.out can be extremely large (tens of GB). Therefore, can we add a option to determine whether to output d.out?

[brucefan1983]

Thanks for the nice suggection. I will check it at some point.

[hityingph]

After discussion with Zheyong, this issue is not very urgent. Maybe he will fix this problem when he begin to work on BTE module.