Add KPOINTS File Output

This commit gives VaspCat the ability to output KPOINTS files.
Currently, the user can specify mesh generation by the Monkhorst-Pack
scheme (point_mode = 0) or Gamma-Centered scheme (point_mode = 1).

If the Monkhorst-Pack scheme is used, the user can change the mesh size
by altering the mesh_x, mesh_y, and mesh_z options.  Additional dictionary
keys were added to settings.py to reflect these changes.

CHANGELOG:
- Added vaspcat/core/kpoints.py module to save KPOINTS files.
- Modified vaspcat/backup.ini and vaspcat/default.ini to include
  new KPOINTS option names.
- Modified vaspcat/output.py to call vaspcat/core/kpoints.py main
  method.

TODO:
- Fix pdb reading bug in vaspcat/extend/filetype.py where atom names are
  improperly read due to extra letters added as labels.
- Fix issue with installing VaspCat due to new version reading scheme.
- Transition docstrings to Sphinx rst format.
- Document and add boilerplate text to modules missing these docstrings.
- Add additional INCAR options depending on demand by program users.