* splash/SplashBitmap.h:
        * utils/pdftoppm.cc: Add the following features to pdftoppm
          - if omitting input filename or using - for input filename
            reads pdf from stdin
          - if omitting output filename, prints output to stdout
          - create image of a cropped rectangle of the pdf
          - scale pdf to fit in a square of wanted size
        Patch by Ilmari Heikkinen <ilmari.heikkinen@gmail.com>