- XS.Root: root class, allows to use Root.subclass()
- _transactional_fetch(): only get transaction id from options._t
- Transaction..get_emit_options(): emit event 'tid' when a transaction id is generated
- Transactions..get_transaction():
  - Comment-out unused code for __t option
  - Take into account 'fork' transaction attribute, which requires transaction to be forwarded
  - Handle Transaction event 'tid': WIP
- Add Documentation