Routing Callback

[trafnar]

In order to make the documentation menu animate correctly, I think I need to know when a new route is being navigated to. Is there a way to trigger an event in this case that can be responded to by the other nav items?

Here's what happens:

• when a section is expanded, the height of the child section is calculated so that it can be animated to (CSS won't animate to 'auto' height).
• when the animation is finished, I will set it back to 'auto' in order to accommodate changes inside it which change its height.
• when another menu item is navigated to, that may cause the current section to collapse, which means the height needs to be set back to a number, instead of auto but I don't know how to hook up an event in that scenario.

[trafnar]

ref #160