Implement simple daily decrement mortality model

[MatthewCaseres]

• Take in state
  • mortality_table_index::Int
  • issue_age::Int
  • timestep::Int # use these things to get the daily mortality rate
  • from::Date
  • to::Date # apply daily rates across from->to to get termination states

[MatthewCaseres]

Ok so this is probably not belonging in this repository but in the LifeSimulator repo in JuliaActuary