Tilings

Added
- add the `can_be_equivalent` methods to `AddAssumptionsStrategy`,
`SplittingStrategy`, and `FusionStrategy`.
- added a `get_assumption` method to `Tiling`

Changed
- the `Factor` algorithm will now factor `TrackingAssumptions` if they span
multiple factors of the tiling. This means that the `SplittingStrategy` is
removed from the tracked `StrategyPack`. It does not factor
`ComponentAssumptions`, so using this strategy still requires the
`SplittingStrategy`.

Fixed
- remove empty assumptions when creating extra parameters in `FusionStrategy`
- the method `Tiling.get_genf` returns the Catalan generating function for Av(123).
- correct the generating function equations for `SplittingStrategy`

Removed
- Removed optional arguments from the `from_bytes` method on `Tiling`

Added
- add a new `AddAssumptionStrategy` which adds an assumption to a tiling.
In practice, when expanding a class, we actually remove an assumption to
determine which rules to add.
- the `get_equations` method is now implemented for the strategies
`AddAssumptionStrategy`, `SplittingStrategy`, and `FusionStrategy`.
- the `extra_paramters` method was implemented for symmetry strategies,
allowing these to be used when enumerating tracked trees.
- Add the `InsertionEncodingVerificationStrategy` which verifies n x 1 and
1 x n tilings which have a regular topmost or bottommost insertion encoding.
- Added the `SumComponentAssumption` and `SkewComponentAssumption` giving the
ability to track specifications using component fusion.
- add partial flag to `insertion_point_placements` and
`insertion_row_and_col_placements`
- Allow fusing rows and columns which are positive on either or both sides.
- The tracking of interleaving factors is implemented, including the poly time
algorithm. This includes the new strategy `AddInterleavingAssumptionFactory`
which adds the assumptions required in order to enumerate when performing
an interleaving factor strategy.
- The `TileScopePack` has a new method `make_interleaving` which by will change
any factor strategy in the pack to allow interleaving. The default setting is
for tracked, and so the assumption strategies are also added. This can be
turned off with the flag `tracked=False`.
- The `possible_parameters` method on `Tiling` allowing for sanity checking
specifications with multiple variables.
- `InsertionEncodingVerificationStrategy` was added to verification expansion
packs.
- `forward_map_assumption` method on `Tiling`.

Changed
- The definition of a local `TrackingAssumption` in `LocalEnumeration` now says
it is local if every gp in it is local (before it was they all used the same
single cell).
- the default in `LocalVerificationStrategy` is now `no_factors=False`.

Fixed
- untracked fusion packs don't add assumption strategies
- the length parameter for `all_the_strategies` is passed correctly to the
requirement insertion strategy.
- use fusion on positive `Av(123)` when expanding 1x1 verified classes
- fix bug that prevented applying all eight symmetries
- fix assumption mapping bug in `FusionStrategy`
- fix `__repr__` in `FusionStrategy`

Added
All the necessary strategies for combinatorial exploration.

Changed
Refactoring and speed up of many algorithm most notably the is empty check.

Removed
- Support for Python 3.5 and earlier

Changed
- Update dependency versions

Changed
- Update comb_spec_searcher to 0.2.1

Added
- Remove factors from requirements if already implied by other requirement
list.
- Added tiling method `is_empty_cell` and `is_monotone_cell`
Changed
- The `cell_basis` method of the tilings has an 1 obstruction for empty cell.
The basis of a cell that is outside of the tiling is no longer defined.
- The requirement list in `cell_basis` method now finds intersections of
requirement lists
- New `add_list_requirement` method to `Tiling`.
Fixed
- Infinite recursion issue in get_genf.
- Close mongo when finished.