Redo Bugfix #1: Atoms not Appearing

This commit adds a new file, spacegroup.py, originally from the open
source program cif2cell.  It contains a dictionary mapping Hall symbols
to a list of general position equations.  These equations are then used
by posext.py to find the coordinates of every atom in the original cif
file.  Duplicate coordintes are removed by the same method as in the
original bugfix.

The intention of this change is to make how the program finds new atoms
for a given space group more reliable then relying on a bonding
variable that may or may not be found in a given cif file.
Change lattice vector basis equation

Fixed a bug where cif and pdb files saved by VaspCat gave incorrect
basis vectors.  This impacted unit cell shape when the exported POSCAR
file was visualized in a program such as VESTA.

This commit fixes the problem by changing one of the angles in the basis
equation from beta to gamma.  It also switches the equation for
coordinate a13 with that of c31.
Change POSCAR output format

This commit modifies poscar.py so that the output POSCAR file includes
two new types of information:

- Atom type cooresponding to a given atom count
- Fixed coordinate tags next to fractional coordinates

Future revisions will aim to give more control to the user over the
information included in the POSCAR file.
Update lattice vector basis equation

Further updates the equations converting cell parameters to unit cell
basis vectors by taking the transpose of the original matrix.  This fix
was tested with a cif file which previously gave the correct coordinates
in the wrong order.

The code contained in this commit fixes the problem, and it is not
anticipated that further updates to the unit cell matrix will be needed.