Next major version

[baggepinnen]

• Time instead of index (or in addition to?)
  • Filters to store Ts. If default Ts::Int = 1, we can have t be time without breaking the interface.
• initial state distribution part of filter or argument to forward_trajectory etc.?
• Remove df from AdvancedParticleFilter`
• Add input argument for known disturbance? Either always, or depending on a field in the filter. Possibly, let u be of any type, most of the time it's just forwarded to the correct function that is supplied by the user. The dynamics can already now be coded to take, e..g., u::Tuple, u::NamedTuple, u::CustomStruct or whatever. test UKF with non-array u #138