Ciw

+ Fixes bug in PoissonIntervals distribution where if the last rate is zero or so small there is no samples, the cycle begins again too early.

+ Adds a new method for the `simulate_until_max_customers`: "Complete" simulates until a specific number of completed customer journeys; while "Finish" simulates until a specific number of customers have reached the exit node (through bailking or reneging).

+ 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.