Concepts

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Fixed a possible encoding issue with ``.tofile()``.

Visualize more examples.

Added tests for formats dump/load file roundtrips.

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Changed context ``__eq__`` test with non-contexts from ``TypeError`` to ``NotImplemented``.

Fixed non-working augmented assignment operators on definitions.
Simplified definition implementation.

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Added context definition objects, allowing interactive building, modification,
and combination of context creation arguments.

Added ``include_unary`` option to logical connectives calculation.

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Made derivation code more explicit. Subset test replaced by inlined
implementation using only ``bitwise_and``.

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Changed context ``._lattice()`` to a generator.

Fixed failure to handle contexts with single object/property.

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Improved context/lattice division of labour: context now computes all concepts
with their covering relation, while lattice only builds/decorates the object-
based representation.

Improved context and bitset interface used by lattice (``reduce_and()``, ``reduce_or()``).
Added ``doubleprime()``-method to extents and intents.
Added ``raw`` option to ``intension()``, ``extension()``, and ``neighbors()`` method of context.

Added ``EXAMPLE`` context for repl experiments.