Static build

Static libraries can now be generated for CPU, CUDA, and OpenCL platforms. I wrote a test executable that runs all 3 platforms, and is statically linked against OpenMMCPU_static, OpenMMCUDA_static, and OpenMMOpenCL_static. A static pthreads library linked against the /MT runtime is also provided for windows builds. Note that pthreads is linked statically ONLY on windows. On Linux and OSX, the shared pthreads library is used. 

The resulting ldd confirms static linking:

	linux-vdso.so.1 =>  (0x00007fff7f7ff000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f23859fc000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f23857f8000)
	libOpenCL.so.1 => /usr/lib/nvidia-319/libOpenCL.so.1 (0x00007f23855f2000)
	libcuda.so.1 => /usr/lib/nvidia-319/libcuda.so.1 (0x00007f238498f000)
	libcufft.so.5.5 => /usr/local/cuda/lib64/libcufft.so.5.5 (0x00007f237fe6e000)
	libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f237fb6d000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f237f871000)
	libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f237f65b000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f237f29a000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f2385c30000)
	libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f237f083000)
	librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f237ee7b000)

This commit also fixes linking issues for the CPU platform on Windows due to missing OPENMM_EXPORT macros.