GitLab

Redesigned CustomNonbondedForce to eliminate combining rules and allow the expression to directly use parameters for individual particles.

Free energy plugin added
Plugin will not run w/ Obc or GB/VI forces unless line 2004 of gpu.cpp (gpu->sim.totalNonbondOutputBuffers  = 2*gpu->sim.nonbondOutputBuffers;) is commented in -- working on removing this constraint
Also unit tests for GB/VI currently fail 

Restructured how force and energy computations are done to make it easier to write plugins for the CUDA platform

Examples: now builds CWrappers as a library; modified C builds to use it; added visual studio project to build Argon example in Fortran.
System.h: addForce() wasn't returning the index.

Added doxygenable comment that Langevin friction coefficient is in units of collisions per picosecond (as opposed to picoseconds), which Sherm and I deduced by reading reference implementation and testing extreme values.