At https://github.com/dcolascione/elisp-generators, I've updated my
elisp generator support. Please take a look.

Since the last version, I've added documentation, cl-loop
integration, a few more testcases, and a lexical-binding assertion.

I'd eventually like to integrate this package into
the Emacs core, so I've laid claim to a few symbols in the
global namespace, like next. This package actually defines a generic
iterator protocol, and it'd be useful eventually to define iterator
objects for things like buffers and windows instead of relying on
enumeration callbacks.