Add button to initiate compare selection.

Also fix fragile link.
Add stubs for compare view.
Extract common template code into a shared file.

Reduce copy + paste HTML by 2. Hopefully this code
can be adapted for the compare view as well.
Add start of UI for picking runs to compare.

Add UI for picking a run to compare with.
Change id => base

Both base & head are ID's use better names for things.
Add comment to newish template fragment.
Stub out comparison UI.

Add stubs for the summary and details sections for comparing
two profiles.
First pass at implementing compare().

I'm not totally convinced it is ideal, but it works for now.
Numeric values should be right aligned.

It makes scanning columns of numbers much easier.
Add template fragment for compare details.
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.
Merge pull request #26 from preinheimer/compare-runs

Add compare runs