Add PixelOffsetMode.Aligned for aligned drawing with sharp lines

[cwensley]

In Eto's PixelOffsetMode.None, both Graphics.FillRect(Colors.Blue, 10, 10, 10, 10) and Graphics.DrawRect(Colors.Blue, 10, 10, 10, 10) would draw a sharp-edged rectangle with no antialiasing (sans transforms). In System.Drawing's PixelOffsetMode.None, fills are antialiased unless you offset the rectangle by 0.5 pixels. Unfortunately, if you want to use the same rectangles for both the draws and fills you would have to do extra calculations to account for this such as shrinking the rectangle by one pixel for line drawing. PixelOffsetMode.Half was the usual way to deal with this, however line draws will no longer fall on pixel boundaries unless you offset them by 0.5 pixels yourself.

So, a new mode has been added named PixelOffsetMode.Aligned that makes line draws fall on pixel boundaries, and fills with the same dimensions align with them. So, you can now choose Half when you want fills to be crisp with whole numbers, Aligned if you want lines to be crisp with whole numbers, or None if you want both fills and lines to be crisp with whole numbers.