Testgres

* fix `get_control_data()`;
* fix default params of `default_conf()`;
* remove everything on `cleanup()` by default;
* remove cached initdb dir by default;

* bugfix: pass `allow_streaming` to `default_conf()`;
* allow using `PG_BIN` env instead of `PG_CONFIG`;

* introduced `TestgresConfig`;
* add `log_statement='all'` parameter to `default_conf()`;

* introduced `default_conf()`;
* don't remove `base_dir` if it was provided by user;