Include directory wrong in makefile export

The makefile export (vtkm_config.mk) and the package export (vtkm.pc) set the include directory as $(VTKm_DIR)/include. However, the include files are actually in $(VTKm_DIR)/include/vtkm-${VTKm_VERSION_MAJOR}.${VTKm_VERSION_MINOR}. These should point to the correct directory.