From the commit message:
> This patch allows the user to define various sections that will
> be displayed in notmuch-hello. I tried to keep the section
> description flexible, so it allows different queries for the
> tag buttons and the counts next to them, as well as hiding items
> with zero results.
>  
> The sections are (hopefully) fully editable using customize.
>  
> I have not yet rewritten the saved-searches portion using this
> mechanism, to avoid breaking the configurations of many users.

It contains a lot of code to make the whole thing play nice with
customize, but hey, at least it's (somewhat) user-friendly. :)

I'm also not sure if using plists to describe the sections was a
particularly (e)lispy way to do this, so comments are appreciated.

I'll also work on some tests for this functionality, (if no one
has big, structural complaints about the code).

Cheers,
Daniel