Use relative path so that we properly apply --base-href.

[SamuelMS]

Re-implements changes from #12, since they were backed out due to failing tests.

@ocombe Would you mind reviewing when you get a moment? Thanks!

[sergio-new-developer]

I have the same problem..

[MickL]

I just wanted to make the exact same pull-request. You might add changes to README.md, too. Nearly one year later, why is it not merged?

There is no reason for having a hardcoded path.

[MickL]

@ocombe please accept