This pull request adds new tags - @lag and @NullInitialised - that automate initialisation of attribute values at the start of each simulated period. These tags have been added to attributes wherever it was found that the change had minimal effects on simulated projections. Nevertheless, a fair few attributes -particularly in the person object – continue to lack tags for initialization, as I found that including these either led to model crashes or altered projections. It would be useful to crawl over the attributes that remain untagged, to ensure that their values at the beginning of each period are properly treated, and to omit any associated code inconsistencies.