Created API and reference implementation for ring polymer contraction
Merge branch 'master' of https://github.com/peastman/openmm
Created CUDA implementation of ring polymer contraction
Created OpenCL implementation of ring polymer contraction
Created Python API for ring polymer contraction
Merge pull request #14 from peastman/contraction

Implemented RPMD ring polymer contraction
Improved error messages when an invalid number of contracted beads is specified
Merge pull request #15 from peastman/master

Improved error checking
Fixed a bug caused by conflicting definitions of sum()
Merge pull request #17 from peastman/master

Bug fix to Modeller
Merge branch 'master' of https://github.com/SimTk/openmm