On Windows we have 2 issues with the current wrapper:
1. We can't call the binary directly relying on shebang. Now we
call python and pass the script as an argument
2. Use os.path.join() with all components to derive the right
waf-light location
Simple wrapper to be extended later so people don't have to type the
huge "./modules/waf/waf-light" command. It has a very primitive way to
try to checkout waf submodule if it isn't there.