Changed tuple serialization of booleans from (0, -1) to (0, +1) to be compatible with other bindings

- Serialization: False is 0, True is 1
- Deserialization: null / 0 / "" are False. Anything else is True
- Only the empty string is equivalent to false. The string "False" is considered to be true.
- Added unit tests
Added method Watch(...) on IFdbTransaction interface