Add a nng_stream example paired with a socket server on win/linux

[hugolm84]

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This PR adds a nng_stream example that connects to an arbitrary socket. Either start a new server with ./stream -s <portnumber> or connect to an existing one using ./stream -c <url>

[gdamore]

Thanks for your contribution. I'm going to review this closely before I integrate.

[hugolm84]

Thanks for your contribution. I'm going to review this closely before I integrate.

Hi, I understand that this simple demo might not be compelling enough, let me know if it needs to be expanded.

[gdamore]

I just hadn't got a chance to look at it yet.

[gdamore]

I'm just going to merge this for now. It's a demo. It doesn't have to be perfect. Once it's integrated we can further improve it.