GitLab

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

- MingW, where "WIN32" is set by CMake but the compiler is not Microsoft's (should use _MSC_VER) in that case, and 
- in gcc 4.4 which is fussy about some issues that earlier versions were silent about, such as passing a string constant to a "char*" rather than a "const char*".
I also fixed a syntax error in CMakeLists that showed up in the OpenMM workshop for some unknown reason.

Brook is not currently building correctly; I think it has not yet been fully converted to the getTime() interface needed for variable step integrators.

Modified the API for lots of classes so that the number of particles/bonds/etc. need not be specified in the constructor.

Implemented setting random seed for reference platform, as well as adding it as an option to BrownianIntegrator and AndersenThermostat.

Optimization: introduced a kernel to clear forces at the start of each time step rather than relying on the stream

Implemented dynamic loading of platforms from DLLs.  Also fixed a lot of compilation errors and warnings under Windows.