A wip devdraw protocol interposer for debugging

At some point during the course of developing rjkroege/edwood: Go version of Plan9 Acme Editor, I thought that it would be nice to have a new implementation of devdraw. This seemed like a large enough project that I wanted to have some incremental milestones. The first such milestone was an interposer devdraw that recorded the devdraw protocol to a file while delegating the implementation to the original devdraw.

Sort of works as an interposer. Project is currently on hold.