Use XML to store helpfile content

[wyld-sw]

Copied from latest discussion:

https://www.geeksforgeeks.org/displaying-xml-using-css/
https://webplatform.github.io/docs/tutorials/styling_xml_with_css/

This way, we have our docs in a nice easy to load structured format (Though we will need either an XML lib or to write a basic XML parser -- for our purposes, we could probably just alter the existing man/mpi parser to look for XML tags instead of ~ marks) and we can still load them in a web browser without needing a separate XML format.