[Snek] [keith-packard/snek] a4c380: Add snek-tone.builtin

[Keith Packard]

  Branch: refs/heads/main
  Home:   https://github.com/keith-packard/snek
  Commit: a4c380441ffe76e96a70d62647fa5997dfbc8da5
      https://github.com/keith-packard/snek/commit/a4c380441ffe76e96a70d62647fa5997dfbc8da5
  Author: Keith Packard <keithp at keithp.com>
  Date:   2020-06-12 (Fri, 12 Jun 2020)

  Changed paths:
    A snek-tone.builtin

  Log Message:
  -----------
  Add snek-tone.builtin

This defines the interface for tone and tonefor builtins, along with the
tone.<note> values for frequencies.

Signed-off-by: Keith Packard <keithp at keithp.com>