Features
- Make ErrorType enums compare as strings
([269](https://github.com/Bluetooth-Devices/dbus-fast/pull/269),
[`c6a8301`](https://github.com/Bluetooth-Devices/dbus-fast/commit/c6a8301704162e1c4d07470c32ca0830f531b6d4))
The DBusError exception stores the error type as string. This makes the exception not directly
compare to the ErrorType members (for example DBusError(ErrorType.FAILED, "").type !=
ErrorType.FAILED). This makes ErrorType also a string to make this comparision work.