Feature/map

[dustinvtran]

Summary:

This refactors the Inference class as discussed in #38. This will make it easier down the line for

• new inference methods such as the VAE bound in Feature/vae #49 and hierarchical variational models
• more custom diagnostics such as print progress in use more samples to evaluate and print objective function #40

It also adds MAP, where the user need only specify the model, data, and the transformation from unconstrained to constrained latent variables.

Examples using a Gaussian and the Beta-Bernoulli model are added.

Intended Effect:

N/A

How to Verify:

Run all examples to see that they still work.

Side Effects:

None.

Documentation:

Written in example script.

Reviewer Suggestions:

@mariru, @akucukelbir

[akucukelbir]

it looks good dustin.

but did i already lose the battle re: MAP being a type of VI? could we discuss briefly today before merging at least?