Add support for infinite data traversals

[oubiwann]

This will require managed state for a given matrix (see #63).

Tasks:

• Define initialisation function that will create a worker on-demand, with its own state (very much like the Erlang code that is used to manage TCP connection data)
• Initialisation will include giving the current/starting point and an algorithm to use for traversal (e.g, "random walk")
• Define a "next" functions that takes no options, but uses the current state and initialised data / options to provide the next point in the traversal
• Provide functions for retrieving the set of points defined for the traversal so far
• As for storage, there should be an option to keep all, only the last one, or the previous n points marked as the traversal
• Add function for ending the traversal (and thus killing the worker)

Companion ticket to:

• Add support for finite data traversals #60

Depends upon:

• Support centralised, long-running state data #64
• Add "linear scan" function #54