Liblet

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- Modifications in the display module:
- removed StateTransitionGraph.from_lr method,
- added large_label parameter to StateTransitionGraph.from_automaton method,
- added compact parameter to ProductionGraph.
- added sep parameter to dod2table method,
- added sort parameter to dod2table method (to control sorting of row/column headers),
- methods cyk2table and prods2table generate a bordered (non wide) table,
- added warn method (to display messages on sys.stderr),
- added ff2table method (to display FIRST/FOLLOW table),
- added dict2table method (to display a dict as a table),
- method dod2table encloses cell content in <pre>,
- method dod2table uses OrderedDict.fromkeys to make the list unique preserving column order,
- reviewed table visualization methods.
- Modifications in the grammar module:
- added Item.symbol_after_dot and Item.advance methods,
- improved type checking for Transition,
- Transition can be made from tuples of items,
- renamed Grammar.context_free to Grammar.is_context_free (and added to __slots__).
- Modifications in the utils module:
- added Stack.peek method (to inspect the top of the stack without pop).
- Improved documentation:
- fixed the documentation of the modified methods and classes,
- added documentation for grammar.Item,
- regenerated examples (due to display module improvements),
- uniformed right/left-hand side naming,
- Tests:
- added tests for the Transition containing items,
- added a test for the new Stack.peek method,
- Cleanup:
- moved EarlyItem out of the library (it will not be used soon),

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- The display.Tree.__repr__ method now puts parentheses around all subtrees (leaf included).
- Added rhs_is_suffix_of to Production.such_that and tested the new kwargs.
- Added documentation for Production.such_that.
- Added documentation for Grammar.restrict_to.
- Added documentation for StateTransitionGraph
- Added grammar hygiene and CYK to docs/examples.
- Added Creative Commons license file (for docs).
- Moving the playground here and added a mybinder button.
- Added a custom CSS for tables in docs.

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- Added Stack.copy and Queue.copy methods.
- Made Stack and Queue iterable.
- Changed the __repr__ method of Stack: the representation of Stack([1, 2, 3]) is Stack(1, 2, 3 ↔).
- Changed the __repr__ method of representation: the repr of Queue([1, 2, 3]) is Queue(← 1, 2, 3 ←).
- Added the Zenodo https://doi.org/10.5281/zenodo.2619589 DOI.

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- Added test to take the coverage of the automaton module to 100%.
- Added some type checking to the automaton constructors and static factories.
- Fixed custom comparison method __lt__ against a different type to return NotImplemented.
- Renamed the Quickstart documentation section to Examples.
- Moved the method Automata.coalesce to StateTransitionGraph (as a parameter of from_automata static method).

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- Maintenance release.

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- Added tests to take coverage of the grammar module to 100%.
- Added this CHANGELOG.txt file (and some tools to handle it).
- Fixed display.cyk2table function for the case with a nullable
row.