add public psh.RunningCommand.Start method
add go fmt wrapper script
rename files; all of psh written so far is the command layer.  the friendlier amoffat-pbs/sh inspired layer will be built above the command layer and kept in separate files.
wip checkpoint on the friendly psh.Sh command creation syntax.

lots and lots of closures.  also still littered in debug printfs.
create system to expose data from the closure but only to other parts of the private api.  This means we can attach more functions to the closure, and have them take state from it and make even more closures spawned from that as desired... which, endgame, gives me an API where you can treat the command factory as either an object with methods, or a magic megamethod (and interchangably!), whichever you prefer.