Reynir

* Old test corpora deleted
* README updated
* S inside CP-REL fixed

* Switched from GNU GPLv3 to MIT license, in accordance with the requirements of the Icelandic Government's 5-Year Language Technology Programme
* Python 3.6 is now a requirement; Python 3.5 is no longer supported
* Renamed repository from `ReynirPackage` to `GreynirPackage`
* Many enhancements to the context-free grammar
* Type annotations added
* Added circuit breaker to abandon the parsing of very complex and time-consuming sentences, via a `ParseError` exception
* Documentation additions and formatting improvements
* Added `force_number` parameter to `NounPhrase` class
* Added `error` attribute to the `_Sentence` class
* Many other smaller enhancements

* Lots of type annotations added
* Adapted to Tokenizer 2.1.0 which no longer splits a final period off an abbreviation that ends a sentence
* Significant additions to vocabulary; minor additions to grammar
* Added ability to dump and load `_Sentence` instances, including tokens, to and from JSON

* Added test for foreign sentences, i.e. sentences where less than 60% of the words are found in BÍN (or resolved by the composite word algorithm). Such sentences are now marked by an error code instead of being parsed.
* More flexibility in specifying the maximum length of sentences to be parsed. The (overridable) default is now a maximum of 90 tokens in a sentence.
* Added and enhanced functions for generating lemmas from parsed sentences. New properties include `_Sentence.lemmas_and_cats` and `_Sentence.categories`, and the method `Greynir.parse_tokens()` has been added.
* Grammar and vocabulary improvements.
* Better handling of abbreviations and multi-word prepositions.
* Improved type annotations in the main Greynir API.
* Added tests.
* New features documented and examples added.

* Added type annotations to ReynirPackage's public API; now compatible with the `mypy` static type checker
* Added `BIN_Db.lookup_lemma()` method in `bindb.py`
* Enhanced pattern matching functionality in `matcher.py` and `simpletree.py`
* Various grammar and vocabulary additions

* Added `progress_func` parameter to `Greynir.submit()` and `Greynir.parse()` functions, for progress update callbacks while a parse is ongoing
* Performance regression under PyPy 7.3 fixed by refactoring token/terminal matching code in `binparser.py`.
* Split `matcher.py` and moved `SimpleTree` class to `simpletree.py`.
* Allowed category of word forms denoting prepositions to be restricted via `Phrases.conf`.
* Switched to new-style CFFI callbacks from C++ code to Python for better performance and reliability