Draw scaled text instead of resizing after drawing

[dblock]

The implementation of drawImageFromText used to first draw the text, then resize it, creating something blurry. I removed resizing in https://github.com/dblock/ARASCIISwizzle/commit/4598e98148121c295a53da24f66802984cfe5f4c, but now you get images of different size. If you combine that with a UIViewContentModeScaleToFill content mode, things look really good. We should be able to resize the same way as UIImageView does with scale to fill, without blur.

Furthermore, we should be able to figure out how many characters we need in width, what font size to pick, etc., to get as close as possible to the target size.