Upgrade for Datasette 1.0a20

[simonw]

Has a bunch of breakages.

[simonw]

One key error:

    def introspect_tables(conn, datasette, db_name):
        db = sqlite_utils.Database(conn)
    
        table_names = db.table_names()
        view_names = db.view_names()
    
        table_metadata = {}
        table_namer = Namer("t")
    
        for table in table_names + view_names:
>           datasette_table_metadata = datasette.table_metadata(
                table=table, database=db_name
            )
E           AttributeError: 'Datasette' object has no attribute 'table_metadata'