More work on markdown work-flow

Still need to add pretty printing (the <?prettify?> directive fails.
Also, still need to be able to specify what css and JavaScript files to
insert in <head>.
Use etree to build html file and add prettyprint
Add insert CSS and JavaScript to markdown workflow
Update readme
Add extra css for exercise (for em, strong tags)
Refactor convert-markdown.py
Convert to DOS line endings
Automatically inserts footer
Update convert-markdown.bat with correct .py file