Ciw

+ Allow some numerical imprecision in the PMF probability sums. This allows for very large arrays of probabilities and use of Pandas and Numpy to define probabilities.

+ Allow custom exit node classes.

+ Remove `reneging_destinations`, move to a jockeying routing option within the routing objects.

+ System capacity implemented.
+ Server schedules objects now take `numbers_of_servers` and `shift_end_dates` keywards, instead of `schedule`.
+ Server schedules and slotted services can be `offset`.
+ Added a GroupedNodePopulation tracker.
+ Restructures documentation, adds more guides, and updates reference pages.
+ Routing objects implemented: TransitionMatrix object, ProcessBased object, FlexibleProcessBased object, NetworkRouting object, Direct object, Leave object, Probabilistic object, JoinShortestQueue object, LoadBalancing object
+ Added `reroute` as an option for interrupted preemptive services.

+ Fix bug where Individual's server isn't reset after a slotted service.

+ Allows class methods as generator functions for process-based routing.