Improvements:

- Allow unicode strings where reasonable, in particular for filenames.

- Include C versions of Cython modules in the distribution, removing the
  build dependence on Cython.

- New submodule of Visualization for the molecular viewer Chimera.

Bug fixes:

- NumPy compatibility fixes.

- IO.TextFile: make sure that __del__ closes a file only if it was
  opened successfully

- Geometry.Transformation: ensure that screwMotion returns a positive distance.
 
- Physics.PhysicalQuantities: fix definition of barn.

- IO.NetCDF: replace unsigned long by size_t in C interface to netCDF.

- Functions.Interpolation: more checks on axis arrays.

- DistributedComputing: fixed deadlock in task manager.