Mac/iOS: Add return value to dw_window_set_bitmap(_from_data) in resource refactoring. They now return DW_ERROR_NONE on success, DW_ERROR_UNKNOWN on invalid parameters and DW_ERROR_GENERAL when failing to load the bitmap. This change came when I discovered Xcode UI does not allow subfolders in the copied resources. dwtest has been modified to function in either way... from a compiled app bundle or from the build directory. The API change should not affect apps, but may require changes to other language bindings. Follow ups for the other platforms will be coming shortly.

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