- added `remove_view` API to drop a view
- added `rename_view` API to rename a view
- added `get_view_data` API to get all (or a set) of view data, including names, types, and "appdata" blobs
- added new `UnknownViewname` exception
- map PostgreSQL/psycopg2 `UndefinedColumn` exception to `InvalidAttr`
- map PostgreSQL/psycopg2 `UndefinedTable` exception to `UnknownViewname`