Change VaspCat version to 0.1a3

This commit changes the version number of VaspCat to 0.1a3.  The package
now contains the core functionality needed to output POSCAR, POTCAR,
INCAR, and KPOINTS files.

Minor changes were made to how setup.py gets the version number to fix
an installation bug the program experienced.

CHANGELOG:
- Changed __version__ variable from 0.1a2 to 0.1a3.
- Modified import statement in setup.py to fix installation error.
- Changed MANIFEST.in so settings files are included in program install.

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