Bring back image captions

[pdfkungfoo]

The automatic conversion to Markdown didn't correctly preserve image captions (where these were present in the original HTML), or lost them altogether.

As a reminder, here are the Markdown code options:

# Only image, no "alt" text, no caption
![](./rose_shape.png)

# Image with "alt" text, no caption
![](./rose_shape.png "'Alt' text")

#  Image without "alt" text, but with caption
![Image caption](./rose_shape.png)

#  Image with "alt" text and with caption
![Image caption](./rose_shape.png "'Alt' text")

To get it right, we'll have to look up what's in the original HTML.

[emcconville]

Seems caption is removed if image tag is included in anchor.

[![Image caption](./rose_shape.png "alt text")](./rose_shape.pngl)

Can we verify this behavior? IMHO, I believe that a image linked to self is no longer relevant with modern browser's context menu (ie right click, and open image)