State Introspection API

[MatthewARinehart]

Why

As a Manticore user, I'm frustrated by Manticore's apparent inactivity while it's running. If no warnings or debug messages are generated, I can't tell whether Manticore is making progress, or simply spinning its wheels.

To fix this, I need an APi that will let me see query what Manticore is doing during execution.

Acceptance Criteria

At any time from a script, a user can:

• List the states and their IDs
• View the current status of a state (Waiting for solver / Waiting for worker / Running / Killed / Terminated)
• View the current program counter for a state and number of instructions executed
• View the amount of time since the last status transition
  Stretch goals:
• Provide a means to subclass the plugin that captures internal state
• Register a callback that's called every n seconds when Manticore is executing

Dev Notes

We'll need to add state transition callbacks to the event system. Then we'll have a plugin running on the main thread that subscribes to all these events and maintains a model of the current state lists that doesn't require jumping across thread/process boundaries.