[CM] (sub)environments and object->string with :readable

[bil at ccrma.Stanford.EDU]

The previous example would have worked; I thought
you were unhappy that it was not simple, but it is
intended for s7's use.  object->string with :readable
and format with ~W are the built-in ways to serialize
most s7 objects.

(The complexity of the previous example came from s7's
attempt to preserve the outlet chain, but the outer
let refers back to the inner one -- a circular reference).