GitLab

Use Doxygen to generate API docs for Python.  This involved lots of changes both to Python API generation and to Doxygen doc generation.

Variable time step integrators correctly report the size of the last step taken.  Also improved accuracy of integration unit tests.

NonbondedForce sometimes included energy terms that weren't appropriate to the specified force groups

NonbondedForce sometimes included energy terms that weren't appropriate to the specified force groups

Eliminated having CMake run programs to check for CUDA and OpenCL compatible GPUs.  They mostly just caused problems.