Treedb

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Format timespan years with 4 digits.

Refactor recursive tree queries to improve code sharing.

Simplify stats query and ``iterdescendants()`` query.

Stats.ipynb: fix n_descendants query, add count to min/max boxes, plot more
frequency distributions.

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Fix default root (change from . to ./glottolog/ as documented).

Fix ``treedb.write_json_lines()`` under Python 3.6 when passed a file object.

Extend showcase notebook and test coverage.

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Add ``treedb.write_json_lines()``.

Use ``lang=None`` outside of the database (checksum change).

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Normalize providers and sites into lookup tables.

Fix exception when config file is not found.

Improve logging: log ``sqlite3.Connection`` to identify in-memory databases,
debug log package location.

Improve tests.

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Fix some aggregation orders in ``get_json_query()`` that depended on the
insertion order.

Fix ``get_query()`` link markup. Use the same aggregation order as
``get_json_query``.

Fixed ``treedb.iterdescendants()`` to include roots with no descencants.

Improve ``treedb.print_languoid_stats()`` performance and the query used for
the ``stats`` view.

Reduce file size adding WITHOUT ROWID to tables with non-integer or composite
primary keys.

Stabilize ``treedb.print_query_sql()`` notebook output with ``flush=True``.

Change ``__dataset__`` and ``__producer__`` primary key from ``BOOLEAN`` to ``INTEGER``.

Use ``sqlite.sqlite_version`` instead of querying the engine.

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Build with Glottolog ``v4.2.1`` per default.

Improve ``treedb.print_schema()`` output for views.

Improve tests and logging.