Implement some more of the comparison view.

* Fix incorrect math.
* Implement absolute difference in summary panel.
Add more data to compare page.

* Cache functionCount as it isn't cheap to compute, and we need it a few
  times.
* Fix mistakes.
Add some lipstick.

* Add colouring to function count changes.
* Add number formatting.
Fix mistakes and add tests.
Remove things that don't work for now.

I'll add % differences to everything later.