Fixed anchor links being hid behind fixed header

The solution for this is to add anchors as <a> tags with the
`.anchor` class like so:

    <a id="some-anchor" class="anchor"></a>

The anchor class will cause the anchor tag to be offset 50 pixels
up from its location, fixing the issue.
Merge pull request #9 from smart-facility/fix-anchor-offset

Fixed anchor links being hid behind fixed header