initial commit - based on current quantum input files in SfePy
nitrogen input with modified potential (no singularity)
minor tweaks, plotting potential
nitrogen: added DFT-related stuff
use norm_l2_along_axis()
added n_electron option
nitrogen: use output_dir, log DFT iterations into log.txt
nitrogen: iter_fig_name option
nitrogen: boundary conditions for the Poisson equation (V_H)
ignore all subdirs
nitrogen: added sgscipy and scipy_lobpcg eigensolvers, Q1 mesh support
nitrogen: workaround r = 0 singularity in potential
nitrogen: added hooks, probing results, fixed for refactored Mesh coordinates

- added def gen_rays(), iter_hook(), post_process()
- Mesh.nod0 -> Mesh.coors, Mesh.ngroups - Mesh.coors.shape[1] == dim
nitrogen: added nls.scipy_broyden_like solver (for DFT)
nitrogen: works with probe.py, added gen_rays(), probe_hook()
nitrogen: ray probes and probed data saving
nitrogen: small updates
nitrogen: update for physical QPs
nitrogen: update for probe.py saving the data
nitrogen: fix the V_H equation right-hand side