#20 Rasterize page

[Han]

Motivation: This can be very useful for those e-ink readers. Most of the readers on the market are not able to render all pdf files without any error. It would be very useful to render the page on computer, save it as an image and export again as pdf. This would circumvent the limitation of the reader, since they all can display a pdf page containing just image.

Function: When exporting the page, not the original page but a rendered image of the page is saved in pdf. The rotating/cropping configuration is considered. Also the user can choose the desired image resolution (dpi) and color depth.