Hopwood-HowToMakeErrorHandlingLessErrorProne.pdf was the wrong file (.odp instead of .pdf).
That'll teach me to be more careful using git while still jetlagged.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>
Merge pull request #30 from noether-lang/master

Hopwood-HowToMakeErrorHandlingLessErrorProne.pdf was the wrong file