dvsim sometimes fails with an error about relative links #227

I can't remember the exact error, but when it's trying to work out relative links from the summary markdown to the HTML, the markdown reporter defaults to using the CWD as the relative_to directory (which is a terrible default), and if that isn't a subdirectory of the other path then it fails with an exception.

Possible fix here: df68de6

I mean it fixes it for me but may not be the best solution.