Betfairdatabase

Improvements
- `DatabaseDirectoryError` is raised when a database directory is not a directory or it does not exist.
- Command line application catches errors and prints meaningful error messages.

Bug fixes
- Unparsable market catalogue files do not break indexing and inserting.

Improvements
- `insert` method handles duplicate files.
- Python 3.12 support added.

Improvements
- Added `clean` method for removing entries with nonexistent files.

Improvements
- New `insert` method for updating the database with new files.
- Object-oriented interface through `BetfairDatabase` class.
- New generic fields: `localDayOfWeek`, `localDayOfWeek`, `localMarketStartTime`.
- New racing-specific fields: `raceId`, `raceTypeFromName`, `raceDistanceMeters`, `raceDistanceFurlongs`.
- `export` method accepts both directories and files as a destination.

Bug fixes
- Decode market catalogue files as UTF-8.