The decoding attribute for Markdown images

Starting with version 0.7.0, markdown-it-fitmedia will allow to set the decoding attribute of images. At first, I set the default value to decoding="async", but to be defensive, from version 0.7.1 on the default value will be decoding="auto", which is the browsers default behavior.

Dave Rupert lists attributes to be carried by img tags in his blog entry Markdown images are an anti-pattern. markdown-it-fitmedia will set those attributes for your Markdown images.