Prepare particle filter data

Prepare data for use with the particle filter. This function exists to make explicit how time changes through the model relative to the data and to odin's internal clock.

particle_filter_data(data, start_date, steps_per_day)

Arguments

data	A data.frame of observed data. There must be a column date, containing dates (or ISO-formatted strings for conversion with as.Date.
start_date	The date to start the simulation from. Must be earlier than the first date in data.
steps_per_day	The number of steps per day