net/nng: import version 1.4.0

NNG, like its predecessors nanomsg (and to some extent ZeroMQ), is a
lightweight, broker-less library, offering a simple API to solve common
recurring messaging problems, such as publish/subscribe, RPC-style
request/reply, or service discovery. The API frees the programmer from worrying
about details like connection management, retries, and other common
considerations, so that they can focus on the application instead of the
plumbing.

NNG is implemented in C, requiring only C99 and CMake to build. It can be built
as a shared or a static library, and is readily embeddable. It is also designed
to be easy to port to new platforms if your platform is not already supported.

(khorben)