Msdm

- Major fix to A* implementation in 7a52fa71d7734a3968463919c40cfb3ba18a1627
- Additional table support
- `ImplicitDistribution` implementation
- Implementation of Options Framework (Sutton, Precup & Singh, 1999)

Summary of changes/additions:

- Implemented a `Table` class that allows for a dict and numpy-like interface with numpy array backend
- `MarkovDecisionProcess` and `PartiallyObservableMDP` algorithms return `Results` objects with attributes in the form of `Table`s (e.g., `state_value`, `action_value`, `policy`) - note that this is a breaking change
- For all MDPs and derived problem classes, `is_terminal` has been changed to `is_absorbing`
- `FunctionalPolicy` and `TabularPolicy` classes introduced
- `PolicyIteration`, `ValueIteration`, and `MultichainPolicyIteration` have been (re-)implemented
- Tests have been streamlined
- Organization of core modules has been streamlined

Summary of changes/additions:
- RMAX implementation
- Fix TD Learning bug
- Fix `TabularMDP.reachable_states`
- New tests

Summary of changes/additions:

- `LAOStar` error handling
- New `DictDistribution`methods
- New `condition`, `chain`, and `is_normalized` methods in `FiniteDistribution`

Summary of changes/additions:
- POMDP solvers:
- `FSCBoundedPolicyIteration` (new)
- `FSCGradientAscent` (minor changes)
- Planning algorithms
- Major refactor of `LAOStar` to support event listener pattern (note **interface changes**)
- Minor refactor of `LRTDP` to support event listener pattern
- Core classes
- Fix to `TabularPolicy.from_q_matrices` calculation of softmax distribution
- Minor changes to core POMDP implementation
- New domains
- `GridMDP` base class and plotting tools
- `WindyGridWorld` MDP
- clean up

Minor changes