title: How to resize svg image file using librsvg Python binding
body: <p>When rasterizing svg file, I would like to be able to set width and height for the resulting png file. With the following code, only the canvas is set to the desired width and height,  the actual image content with the original svg file dimension is rendered in the top left corner on the (500, 600) canvas.</p>
  
  <pre><code>import cairo
  import rsvg
  
  WIDTH, HEIGHT  = 500, 600
  surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, WIDTH, HEIGHT)
  
  ctx = cairo.Context(surface)
  
  svg = rsvg.Handle(file="test.svg")
  svg.render_cairo(ctx)
  
  surface.write_to_png("test.png")
  </code></pre>
  
  <p>What should I do to make the image content same size with cairo canvas? I tried</p>
  
  <pre><code>svg.set_property('width', 500)
  svg.set_property('height', 500)
  </code></pre>
  
  <p>but got</p>
  
  <pre><code>TypeError: property 'width' is not writable
  </code></pre>
  
  <p>Also documents for librsvg python binding seem to be extremely rare, only some random code snippets on cairo site.</p>