Rewrite the info about preparing a snapshot to make sense.
Add input_NONE and use it in process_user_input.
Discovered what $800F, $8011 and $8013 do.
Make all block-level comments be 'labels'.

* Split descriptions after ' -- ' and use the explanation for a 'D'.
* Get rid of all 'unk_' prefixes. Always use byte_ or word_.
* Make all descriptions be label_style.