Name a module after the software it provides, not the functionality it
provides.  This allows alternative software providing the same
functionality to be located in Sovereign.

Make a clean distinction between Debian 7 and Debian 8.  Anticipate the
next Ubuntu LTS release (Xenial) that is planned for support.

Writing clarifies thinking and leaves behind guidance for future
maintainers.  Design descriptions shouldn't be required, though,
especially for trivial modules.

Users expect role authors to make decisions.  The role author is
supposed to be the expert who knows what choices to make on behalf of
the user.

I probably got this wrong, but I'm putting a stake in the ground based
on work I've done on the Roundcube module and adding Let's Encrypt
support to the common module.

Conflicts:
	CONTRIBUTING.md

added details about the license and the supported distributions.

Reflects the move to the `sovereign` GitHub organization.