First step toward porting a real HarfBuzz demo

Hi. This is first step toward porting [this](https://github.com/ebraminio/glcourse/blob/master/tut1.c)! But I hope it would be in right direction! It needs making [SharpFont.Face.Reference](https://github.com/Robmaister/SharpFont/blob/master/SharpFont/Face.cs#L728) public! I am not sure how to avoid it and don't know how to convert array of C struct to csharp currently but I hope you would help :-)