Add SMC example

[fritzo]

We can use pyro.markov to trigger an optional resampling step based on perplexity. This behavior would be handled by an inference handler.

Outline

• [ ] Add storyboard example using pyro.markov to perform SMC
• [ ] Implement SMC handler to interpret pyro.sample statements as multi-particle samples
• [ ] Implement resampling by interpreting pyro.markov statements

[fritzo]

@eb8680 Do I understand correctly that this is blocked by #52 and #50 ?

[eb8680]

Yes, I think so. We might also need to update minipyro.