feat/retain md image links

[shreyanid]

Unstructured doesn't currently retain markdown image links (like this format). User wants to do document loading through Langchain with Unstructured and keep markdown image links.

[Donglong]

When will this feature be supported?

[beiyanpiki]

+1. It is beneficial to extract the src and alt attributes of an image in Markdown to metadata in certain scenarios. Hope Unstructured can support this.