Functions for Epidemiological Analysis using Population Data

 Enables computation of epidemiological statistics where e.g.
 counts or mortality rates of the reference population are used. Currently
 supported: excess hazard models, rates, mean survival times, relative
 survival, as well as standardized incidence and mortality ratios (SIRs/SMRs),
 all of which can be easily adjusted for e.g. age.
 Fast splitting and aggregation of 'Lexis' objects (from package 'Epi')
 and other computations achieved using 'data.table'.