...without preventing clicks on other things.
Just use an `<a name="...">` tag that doesn't take up any space to make sure that we're not covering up something else.
For whatever reason, doing `position: relative; top: -$navHeight;` doesn't work and causes the anchor target not to be moved up. This solution works in both Chrome and Firefox.
Fixes#447.
We do this by moving the actual anchored element up in the page without moving the actual text. (Apple uses a similar trick in their framed docs.) Now this looks a bit sillier on smaller screens but it's better overall.
This gives markdown headers an id so that we can link directly to
sections of our docs. This is better than the alternative of adding them
all ourselves.
