re-Define DOS

[ghost]

rather than automate the plot of DOS, it is much more flexible if get the DOS data and energy mesh.

[ghost]

It happen this to be my first pull request. So i forgot another things, to make my new DOS function works, we need to call statsbase package.

so we need to add

using StatsBase
export get_DOS

thanks

[cometscome]

Hi @muhammadgaffar

Thank you for sending the pull request.
I added get_DOS function in the latest version.
Since one might use plot_DOS, I added get_DOS as an additional function.
Thank you.