In the spirit of making CL-Protobufs represent exemplary modern Common Lisp code:

In the spirit of making CL-Protobufs represent exemplary modern Common Lisp code:
 - Use 'defparameter' instead of 'defvar' where appropriate.
 - Fix 'defvar' doc strings to distinguish between globals and "thread locals".
 - Avoid using 'nconc'. introduce a new 'appendf' macro instead.
 - Add a comment lamenting the fact that exporting something like 'proto-options'
   also exports the writer '(setf proto-options)'. Fixed in Dylan.