Made the database connection reusable rather than recreating it every time.

Fixed typo in output.

Ensured that maximum and minimum column length assertions are only asserted where actually relevant.

Rewrote provideColumnLengths() to return fixed rather than variable-length result.

- Improved descriptive output. ...

- Added sqlifyValue function to improve flexibility of SQL string handling.
- Renamed 'type' property to 'sql_type'.
- Added 'generic_type' property.
- Improved testing of legal and illegal values.

Added preliminary output based on whether an illegal value is rejected by a constraint or an actual overflow.

- Slightly tidier printing of messages involving plurals. ...

- Now properly handles both "check constraint violated" and "value larger than specified precision" errors.

Added experimental unit testing code.