* Uncommenting the networkDelay in sendPtyOutput exposes a bug in
  the Activity chain construction.
* potential DOS where developer sends Activity Entered that all
  refer back to the first Activity Seen. This requires the user
  side to keep a Backlog containing all later Activity Seen, so uses
  up a lot of memory.

  For this to work, the developer would need to include
  in their Activity Entered echoData anticipating all the Activity Seen
  that they have generated. This is doable; for example the developer
  can send a stream of A's, and then needs to only include the right
  amount in the echoData.

  Should probably cap the BackLog to some maximum size to prevent
  this kind of DOS. Dropping old items from the BackLog after some
  amount of time would also work; after eg 10 seconds it's very
  unlikely that a Activity Entered will legitimately refer to an
  old backlog item.
* Include Entered in the Activity chain, so when the developer makes
  2 keypresses close together, they send the second Activity Entered with
  the first Activity Entered as its HashPointer. This allows the developer
  to prove the order they did things.
* Encryption!
* Network!
* Server!
* gpg key downloading, web of trust checking, prompting
* log Activity, and make a program to a) validate the log and b) display it
  with graphviz