Add support for cross-reference links in descriptions

[amykyta3]

Enhance to allow references to other nodes from within the description
Probably the cleanest way is to use the existing Markdown syntax for links, but use a distinct URI scheme prefix for regmap paths (like "rdl://path.to.thing" instead of http:, ftp:, etc.)

This would be pretty straightforward to post-process and replace with proper links to nodes/fields/etc