Document dynamic Callable API

[philippjfr]

Our DynamicMaps wrap any callback that is passed in, in a Callable class, which performs memoization of the last returned value and also allows declaring the inputs to the function. Furthermore the callable allows traversing the call-graph of a DynamicMap. We should add a section to the DynamicMap tutorial to explain these details about Callable and how to work with them directly.

[jlstevens]

There is a lot of material to cover in the tutorials if you include streams. We should consider the different ways we might want to split it across tutorials.

[jbednar]

Presumably this would be where we explain how to deal with streaming data, i.e., something dependent on external data sources that update without our actions? Would we suggest adding a "counter" or "timestep" parameter that is ever-increasing to force the memoization to be bypassed, or should there be a more direct method?

[jlstevens]

I've been discussing various ways memoization could be disabled with Philipp. I would prefer to do so in a more direct way than adding parameters just to keep changing the arguments..

[jlstevens]

We'll see if we can add a little more documentation for 1.8.1.