GitLab

1) Added DLL export macros to many classes; enough to get tests to compile
2) Cosmetic changes to reduce warnings in Visual Studio:
   a) change many "for (int i ="... to "for (size_t i ="... to avoid unsigned mismatch warnings
   b) included many explicit static_cast<OpenMMReal>() casts to document places where double->float conversion warnings occur

Added INCLUDE(Dart) to OpenMM CMakeLists.txt

Continuing to implement ReferencePlatform (implemented GBSA kernels, added test case for SHAKE and fixed some bugs in it)

Continuing to implement ReferencePlatform (implemented kinetic energy calculation and LangevinIntegrator)

Created a test case for StandardMMForceFieldImpl's findExclusions() method.  Fixed some bugs that it found.  Created a CMake script and configured it for building and running test cases.