Win: Add support for building the C++ dwtestoo with Visual C. Need to use dwmain() macro instead of standard main() entrypoint for Windows. Had to move the _dw_convertargs() definition outside of the dwmain() macro. The macro can be called from C++ code changing the function definition.

# Set these here to change the version for all platforms
DW_MAJOR_VERSION=3
DW_MINOR_VERSION=3