Ciw

+ Small refactor to Node adding new servers, and to Individuals receiving the Simulation object.
+ Add a library of custom behaviour to docs
+ Support Python 3.8, update hypothesis

+ Ability to incorporate customer behaviour Server and Individual classes.

+ State Trackers slightly more efficent, they do not record any state changes that result in the same state as before.
+ Add the NodePopulationSubset tracker.
+ Distribution objects can now see the Simulation object, for true state dependent distributions.

+ State Trackers now track history
+ State Trackers give state probabilities
+ A number of performance improvements
+ Fix some documentation
+ Test on PyPy3.6 and Python 3.7 too

+ setup.py now finds packages to fix pip install bug

+ Large refactor:
+ Drop support for Python 2.7, Python 3.4.
+ Update networkx and pyyaml requirements.
+ Refactor time so that `Simulation` has `current_time` attribute.
+ Change Transition_matrices keyword to routing.
+ routing can take a process-based routing function.
+ Refactor distributions to be objects: ['Exponential', 0.5] -> ciw.dists.Exponential(0.5).
+ Distribution objects can be manipulated with +, -, * and /.
+ All keywords lower case to conform to Pep8.
+ deadlock_detector keyword takes object, not string.
+ tracker keyword takes object, not string.
+ Add tests and docs to show how objects can be used for state-dependent distributions.
+ All user facing api now takes float('inf') not 'Inf', expect for .yml files.
+ Reference Ciw paper in docs.
+ Add AUTHORS.rst to docs.