Simple interface to specifying models in DiscreteDP

@oyamad This is just a wish list idea that I'm noting down while I think of it. (Perhaps other people have mentioned it too.)

It would be nice to have an interface to specifying discrete DP models for DiscreteDP by a simplified version of what @albop has built for dolo:

http://dolo.readthedocs.org/en/doc/modeling_language.html#example

The interface would allow you to easily specify

• the feasible state action pairs,
• the transition probs
• the rewards for each state action pair

A numbafied routine would map that specification to an instance of DiscreteDP.

This code would be greatly simplified and more attractive to users: http://quant-econ.net/py/aiyagari.html

Same goes for the Julia side.

Start by reading the DiscreteDP implementation and the linked dolo modeling-language example. Define the scope of a simplified model specification for feasible state-action pairs, transition probabilities, and rewards, then determine how it would map to a DiscreteDP instance and whether the proposed Numba and Julia interfaces belong in this issue.