------------------
Added
+++++
- ``Results.get_states`` method - returns state at time ``t``
- Accuracy tests for all algorithms
- Additional consistency checks for ``X0`` and ``k_det``
Changed
+++++++
- Refactor algorithms into sub module ``algorithms``
- Refactor algorithm independent tests
Fixed
+++++
- Indexing issue in propensity calculation in ``direct`` algorithm
- Indexing issue in propensity calculation in ``tau_leaping`` algorithm
- Address edge case X->2X in ``tau_adaptive`` algorithm