BREAKING CHANGE: the bigquery `current_database` method returns the `data_project` instead of the `dataset_id`. Use `current_schema` to retrieve `dataset_id`.  To explicitly list tables in a given project and dataset, you can use `f"{con.current_database}.{con.current_schema}"`

BREAKING CHANGE: `list_databases` is removed; use `list_schemas` instead

BREAKING CHANGE: `zeroifnull` is removed; use `fillna(0)` instead

BREAKING CHANGE: `nullifzero` is removed; use `nullif(0)` instead

BREAKING CHANGE: replace `ibis.show_sql(expr)` calls with `print(ibis.to_sql(expr))` or if using Jupyter or IPython `ibis.to_sql(expr)`

Remove HDFS integration from the impala for dramatic simplification of the backend.

Also move away from an ancient version of impala that is no longer maintained.

The primary motivation here is to reduce the scope of the Impala backend, and to lower its maintenance by supporting fewer features.

BREAKING CHANGE: Direct HDFS integration is removed and support for ingesting pandas DataFrames directly is as well. The Impala backend still works with HDFS, but data in HDFS must be managed outside of ibis.

Co-authored-by: Deepyaman Datta <deepyaman.datta@utexas.edu>

Co-authored-by: Phillip Cloud <417981+cpcloud@users.noreply.github.com>

…date values

BREAKING CHANGE: Columns with Ibis `date` types are now returned as object dtype containing `datetime.date` objects when executing with the pandas backend.

…pstream

…ime64 values

…mmits and allow squash merges

Otherwise, we're stuck telling people to always start PR descriptions
with a blank line which seems silly (and annoying).