Refactor Transponder implementation to be generalized

[eudaimos]

The goal of a Transponder is the ability to attach Promise handling to a network.

Currently the Transponder reimplements a Channel within itself and acts exactly like a channel except for the signaling to its promise.

Desire: reimplement the Transponder to work with any Network interface and compose it with Channel to get the current behavior, but also allow it to be attached to any Network interface for promise integration.

This will affect the @tao.js/koa package which depends on using a Transponder. However that package has not been tested or used yet.