Fix anchorlinks using Hugo link render hooks (#25)

Hugo link render hooks contain a variable reference to the current page.
Using this we can prepend the current page's path to header anchor
links. This fixes the issue where all anchorlinks for headers link back
to the site homepage.

Author: sbsparrow

site/layouts/_default/_markup/render-heading.html

@@ -0,0 +1,4 @@
+<h{{ .Level }} id="{{ .Anchor | safeURL }}">
+  {{ .Text | safeHTML -}}
+  <a class="anchor" href="{{ .Page.Path }}/#{{ .Anchor }}">#</a>
+</h{{ .Level }}>

site/layouts/docs/single.html

@@ -31,7 +31,7 @@ <h1>{{ .Title }}</h1>
 				{{ partial "sidebar/docs-toc.html" . }}
 			</nav>
 			{{ end -}}
-			{{ partial "main/headline-hash.html" .Content }}
+			{{ .Content | safeHTML }}
 			{{ if .Site.Params.editPage -}}
 				{{ partial "main/edit-page.html" . }}
 			{{ end -}}