Mixing methods

[zerothi]

Describe the feature Add mixing methods

• [x] Add linear mixing
• [x] Pulay mixing
• [ ] Broyden mixing
• [ ] Allow complicated mixing methods
• [ ] Use asyncio for writing SCF information either to stdout or logger files

[zerothi]

This is partly, done.

Note, that routines will change to adapt complexity... This will continue in the coming future.

[zerothi]

More or less done, Broyden missing, but... One can do complicated mixers.