hgbook: chapter on templates

[Jordi Gutiérrez Hermoso]

On Mon, 2016-07-18 at 17:58 +0200, Mathias De Maré wrote:
> it's been quite a while since I sent around another chapter. I'm
> afraid I had other topics to focus on. I've reworked the chapter
> 'Customizing the output of Mercurial' to discuss templates (rather
> than the old '--style' option).

I need to write a bit about how the {label(...)} template command
interacts with the colour extension.

- Jordi G. H.