Create container with port forwarding

[jackgene]

This PR resolves #8 by adding the ability to create containers with port forwarding. The changes are non-breaking:

1. DockerClient#createContainer(...) updated to take a third portBindings parameter that is an array of PortBindings (defaulting to empty array - no port forwarding). (See doc comment for details) of PortBinding.
2. DockerClient#start(...) updated to return an array of PortBindings -indicating the the actual port bindings. This is mainly for use cases where the client makes a request to forward to a random available host port (hostPort=0), such that the client is able to get the actual bound port. If the requested hostPort is non-0, the return value should just be what the client provided.

Changes were made to the Docker JSON model to support this.

[alexsteinerde]

Thanks for the PR.
I'll look into this.
By the way the following fork of this repository implemented a lot more functionality. Maybe you want to check it out as well:
https://github.com/m-barthelemy/DockerSwift

[alexsteinerde]

I just noticed, that this doesn't compile under Linux because the Network framework isn't available there.
Is there a reason to use typed IPv4 and IPv6 addresses there?

[jackgene]

I just noticed, that this doesn't compile under Linux because the Network framework isn't available there. Is there a reason to use typed IPv4 and IPv6 addresses there?

My main reason for using typed addresses (vs just strings) is to try and make it harder for client codes to make mistakes (by passing in arbitrary strings, for instance). I had not considered Linux support, but would like to support it.

Do you happen to know if there are Swift typed IP address implementations other than what's in Network? If not, we can just use strings. I quickly looked through SwiftNIO and didn't find anything.

[alexsteinerde]

I didn't find a typed IP implementation as well. There is the SocketAddress type but that also holds the port and is a too heavy type for this problem in my opinion.