Markdeep
Markdeep is an extended variant of Markdown intended to be viewed in a web browser, as it is implemented via JavaScript which takes a text document (with Markdown syntax and some additional features) and converts it to HTML for display. You simply add a line at the bottom that references the Markdeep script (both the remote copy at its creator's site, and a local copy if present for offline use) and also provides a default CSS presentation for the plain-text version as a fallback.
Enhanced features include converting ASCII Art diagrams into real graphics.
The piece of code you're supposed to add to the end of the document is:
<style class="fallback">body{white-space:pre;font-family:monospace}</style><script src="markdeep.min.js"></script><script src="http://casual-effects.com/markdeep/latest/markdeep.min.js"></script>