Changing the type of 'walk'

- Made 'walk' take as input an action and additional state info
- This is to generalize the code to make it work with both the
	visualizer, and any other monadic action that we might want to
	take in the middle of the sampling process
- Also added a slightly general function to print the n latest samples
	- This calls viz_json and as such needs a way to get from a list of
		any type to a list of Doubles for now