ENH: Atoms length and angles
I made two new method in atoms object (one setter one getter), to manipulate with cell lengths and angles. One is:
set_cell_lengths_and_angles(lengths_and_angles)
which has one parameter wich contains 3 lengths of unit cell vector and 3 angles between them. And second one:
get_cell_lengths_and_angles()
which return the same thing (6 paramters: 3 length and 3 angles).
I added this thing also to Atoms constructor, there is a new parameter cell_lenths_and_angles. It does the same thing.
Well, this is my first contribution to a opensource project, I hope I did not done anything wrong.