Make thumbnail and return (html) path to image

        Parameters
        ----------
        imgfilename_rst : rst
            Image filename (relative path), as it appears in the
            ReST file (coverted).

def make_thumbnail(self, imgfilename_inrst):
        """
        Make thumbnail and return (html) path to image

        Parameters
        ----------
        imgfilename_rst : rst
            Image filename (relative path), as it appears in the
            ReST file (coverted).
        """
        builddir = self.env.app.outdir

        imgfilename_src = os.path.join(DOC_PATH, imgfilename_inrst)

        thumbfilename = self.thumbfilename(imgfilename_inrst)
        thumbfilename_inhtml = os.path.join('_images', thumbfilename)
        thumbfilename_dest = os.path.join(builddir, '_images', thumbfilename)

        im = Image.open(imgfilename_src)
        im.thumbnail(thumbnail_size)
        im.save(thumbfilename_dest)
        return thumbfilename_inhtml