lisp: add put and get primitives, rewrite describe in lisp.

* lib/sexpr/primitive.lua (get, put): New primitives for symbol
property list access.
(describe): Remove.
* lib/sexpr/init.lsp (describe): Rewrite in lisp.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
lisp: fix docstring and an implementation bug for `progn`.

* lib/sexpr/primitive.lua (progn): Fix typos in docstring and
implementation code.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
sexpr: add std.optparse command line option parser.

* sexpr (OptionParser): Import and pass it a help spec. Support
evaluating lisp files as well as REPL.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>