Added GcGraphics.DrawRotatedText() method: Draws rotated text inside an unrotated rectangle (similar to how MS Excel draws rotated text in borderless cells).
Added GcGraphics.DrawSlantedText() method: Draws rotated text inside a slanted rectangle (similar to how MS Excel draws rotated text in cells with borders).
Added GcGraphics.MeasureRotatedText() method: Calculates the bounds of rotated text inside an unrotated rectangle.
