Header links contain backslashes on Windows

[ollie27]

For example, when rendering the book-example on Windows using 0.0.21 the generated index.html contains:

<a class="header" href="misc\introduction.html#introduction" id="introduction"><h1>Introduction</h1></a>

As URLs use forward slashes, it should obviously be:

<a class="header" href="misc/introduction.html#introduction" id="introduction"><h1>Introduction</h1></a>

[Evrey]

Smells like my old issue #119

[ehuss]

I'm going to close as I believe this was resolved a long time ago.