preserve any attributes in <img>

If we have:

  #+ATTR_HTML: :alt my first image :style width: 500px; display: block;
  [[file:image1.png]]

which produces:

  <img src="image1.png" alt="my first image" style="width: 500px; display: block;" />

then we must preserve the extra attributes in
org2blog/wp-upload-files-replace-urls.