investigate: modify iced parser so that"await done defer()" can be abbreviated as "await done".

[davidbau]

The simple case of await, which is to await a single async call that calls back a zero-argument callback, should be simplified to just "await simplecall". In particular, this would allow turtlebits students to write "await done" which makes more sense than "await done defer()".

Should investigate whether the iced parser can be modified cleanly to accomplish this.