v0.8.3

• Fixed bug in __write_default (should have been _write_default)

• API change in close functions, now ret_coord => ret_xyz,
  ret_dist => ret_rij

• Added SparseCSR math operations work on other SparseCSR matrices
  Thus one may now do:

  >>> a, b = SparseCSR(...), SparseCSR(...)
  >>> aMb, aPb = a * b, a + b
  

  Which makes many things much easier.
  If this is used, you are encouraged to assert that the math is correct.
  Currently are the routines largely untested. Assistance is greatly appreciated
  in creating nosetests.

• Geometries now always create a supercell. This was not the case when
  an atom with no defined orbital radius was used. Now this returns a
  supercell with 10 A of vacuum along each Cartesian direction.