Replace Word-generated PDF with Markdown source code

Sean asked me to look through the curriculum for this course.

I've got a few changes to suggest, but it is not very convenient to work from a PDF (or even from Word). This change replaces the PDF artefact with Markdown source code, which can easily be turned into HTML, PDF, and many other formats using [Pandoc](http://johnmacfarlane.net/pandoc/).

It also has the benefit of rendering nicely directly on GitHub.com.

The Markdown content is virtually identical to the PDF content; this merge request does not include my suggested changes. Those will follow in other pull requests later.