Re-add CallingConvention
Re-add CallingConvention

Closes #448

AlexCatarino/pythonnet,dmitriyse/pythonnet,dmitriyse/pythonnet,pythonnet/pythonnet,AlexCatarino/pythonnet,pythonnet/pythonnet,Konstantin-Posudevskiy/pythonnet,QuantConnect/pythonnet,Konstantin-Posudevskiy/pythonnet,yagweb/pythonnet,QuantConnect/pythonnet,QuantConnect/pythonnet,dmitriyse/pythonnet,Konstantin-Posudevskiy/pythonnet,yagweb/pythonnet,AlexCatarino/pythonnet,AlexCatarino/pythonnet,pythonnet/pythonnet,yagweb/pythonnet,yagweb/pythonnet