Second release of 2022 with BSE calculations, updated optim scripts

This is the second release of gpaw-tools in 2022. The most important feature which is added in this release is the Bethe Salpeter Equation (BSE) solution. Users can choose RPA or BSE for the optical calculations. Because the parallelization of the optical calculations is different from the electronic calculations, we can not use the optical calculations in gpawsolve.py with mpirun successfully. If you have large cells and need performance, you must write your script and use GPAW purely. Also, a new optimization script that uses k-point density instead of k-point number is added. Other optimization scripts are updated. Because new keywords are added in this release, we suggest a full update your all machines that have previous versions.

We are also kindly asking you to help us with your issues and pull requests. We have only one rule, try to keep it simple for broad-spectrum users.

Thank you for trying and helping to `gpaw-tools to make it better.

Release notes

• New optimization script optimize_kptsdensity.py for k-point density optimization instead of k-point number optimization.
• optimize_cutoff.py, optimize_kpoints.py and optimize_latticeparam.py have xc_used in parameters list.
• Naming of some of the output files is fixed.
• Bethe-Salpeter Equation (BSE) solution is added to optical calculations.
• 7 new keywords are added for BSE calculations. opttype, optshift, optBSEvb, optbsecb, optBSEminEn, optBSEmaxEn, optbsenumdata
• Si-2atoms-optical example is now running for both RPA and BSE. Previously, its calculation has 2 steps, now 3 steps.
• CONTRIBUTING and CODE_OF_CONDUCT information is added.
• Fix: Show atom numbers starting from 1, not 0.