convert debian packaging to dh-elpa

[David Bremner]

David Bremner <david at tethera.net> writes:

> The main part which needs sanity checking is 
>
>     [PATCH 1/3] emacs: generate notmuch-pkg.el
>
> It may make sense later (after we drop support for emacs23) to make
> our standard install also use package.el. 

series pushed to release, with the debian versioning modified to reflect
an upstream point release