improve extract_images example
improve extract_images example

* added support for images stored as raw deflated pixels (grayscale, RGB
  and CMYK)
* the code is ugly and repetitive, I need to revisit and clean it up
* transparencies are ignored

bernerdschaefer/pdf-reader,tdenovan/pdf-reader,eitoball/pdf-reader,tardate/pdf-reader,alexdowad/pdf-reader,boutil/pdf-reader,yob/pdf-reader,yob/pdf-reader,nifarius/pdf-reader,yob/pdf-reader,gordonbisnor/pdf-reader,3jb/pdf-reader,nmadura/pdf-reader,2potatocakes/pdf-reader