width tag not respected for images

[nschloe]

When including images like

.. figure:: https://nschloe.github.io/quadrature/circle.svg
   :alt: 
   :width: 25.0%

the width tag is not respected. See, e.g., here.

(The bug is also present in the on legacy, see here.)

[dstufft]

I need to check what happens if someone puts a huge image in the output here, but I think this is probably OK.

[mgedmin]

An example of this problem is https://pypi.python.org/pypi/ghcloneall. I'm trying to shrink the asciinema-provided image to 50%, but PyPI strips my width/height attributes. (Warehouse at least applies a max-width: 100% so it's not so bad there.)