enhancement: option to scale images to window width

[david-hodgson-at-sky]

The Problem:
some images in the markdown are very big when generated and need to be scaled down to fit within the print area.

Solution:
Add an option to automatically scale the images to the window width (95%).
Use this to set image width in the HTML / CSS.

Others may value two other relatd options: max height; or max width.

[PeterWone]

There are already several options to control the size of images.

Markdown is rendered as HTML during the print process and you can apply a stylesheet as described in the documentation.

You can also use an HTML tag instead of the Markdown notation, and this allows you to apply a style attribute directly to the tag or specify one or more CSS classes.