cloudflared: init at 2018.10.3

'cloudflared' is a multi-purpose client-side tool for CloudFlare Argo
Tunnel, CloudFlare Access, as well as including a simple DNS-over-HTTP
(DoH) proxy tool as well.

However, 'cloudflared' is NOT available under an open source license.
Furthermore, the exact terms of redistribution (namely, if we are able
to redistribute binaries at all) are not entirely clear to me. As a
result, I have filed the following bug report concerning the terms of
redistribution for the source code and binaries:

  https://github.com/cloudflare/cloudflared/issues/53



'cloudflared' does have source code available, however, and it
encourages users to use 'go install' in order to set it up, in fact (or
download their prebuilt, compiled binaries). So using the source seems
to be encouraged. Even then, I'm still not sure if Hydra can serve these
binaries.

In lieu of a more pointed answer regarding source/binary licensing, and
to avoid keeping this expression in my private tree, I've marked it as
'unfree' (to avoid Hydra serving it in any way) as well as compiled from
source (to avoid any 'redistribution allowed while unmodified' terms
that may crop up).

The dependencies for this build were generated using 'dep2nix'.

Signed-off-by: Austin Seipp <aseipp@pobox.com>