csv2db: Add column indexes on errors table. Use typed_cols and `.to_Col()` to iterate over columns to add indexes on, for the main and errors tables.

sql.py: Added track_data_error(). put_table(): ignore(): Take extra e param for the exception. Use track_data_error() to store the invalid value in the errors table.

sql_gen.py: Join.to_str(): Add newline before and after right table if it's been renamed (and therefore takes up multiple lines)

exc.py: ExceptionWithCause: Store the cause in an instance variable for later use

sql.py: mk_track_data_error(): Rename the errors_table to make the generated SQL less verbose

sql.py: mk_insert_select(): Run sql_gen.remove_table_rename() on table to get just the actual name in the DB

sql_gen.py: Added remove_table_rename()

sql_gen.py: Col: Run `.to_Table()` on table to get just the reference to the table, not any SQL code that defines it

sql.py: Added mk_track_data_error() and use it in cast(). This also ensures that if only one source column's row in the CROSS JOIN violates a unique constraint, other source columns' rows are still inserted.

sql_gen.py: with_default_table(): Added overwrite param to overwrite the table (if it isn't a NamedCol)