Agent class, single list
Make an Agent class so the env can contain a list of Agents, rather than several lists of Agent location, direction, target, handle, etc. These hold the current / runtime agent state in the environment. More "static" information like the Agent initial location, target, list of tasks, start delay, etc should go in a separate class, suggest we call it Task / TaskSpec..? The Env should load this into the agent state at start time. See also #15 (closed) which requires start delay etc.