Generate the docs from a single source

[ajdaniel]

It would be nice if instead of storing in source the Word and PDF versions of the worksheets we could store text only versions (like in MarkDown) and the Word and PDF versions (and maybe even Web too) are published from this single source.

If we use something like Travis, then we can build on a release, or a change.

This will help us maintain versions, allow better collaboration, and also allow translations

[ajdaniel]

The Raspberry Pi foundation do this with their Code Club worksheets https://github.com/RaspberryPiFoundation/curriculum_documentation