- refactored pure SA classes to sa_extra
- refactored Slot and introduce basic KVP management (does not handle yet frame and list)
- moved Lot and Schedxaction from model_core to model_business
- enforce check of gnucash version tables
- fix import of Lot (otherwise issue with Transaction that depends on it)
- handle Numeric type in KVP
- fix import in model_budget
- refactor connect_to_gnucash_book and add alias as open_book
- clarify currency object model in doc
- add an examples folder with some gnucash files and a sample sandbox script to play with
- check on version skips the Gnucash row
- update tests according to refactoring
- update ipython notebook (but not yet retested)