Move network package into iso8583-connection module

[alovak]

After the creation of the https://github.com/moov-io/iso8583-connection module, it should be the new home for the network package.

I am considering removing it from the iso8583 module in two steps:

1. Copy it to the https://github.com/moov-io/iso8583-connection module and deprecate it in the iso8583 module.
2. Remove it from the iso8583 module.

[adamdecaf]

You could always forward the old types to newer ones when you mark them as deprecated. Then callers won't need to immediately change unless they're checking for Deprecated calls.

Example: https://github.com/golang/go/blob/master/src/io/ioutil/ioutil.go

[GalihFajar]

Hi, is this issue still available to work on?