statespacer 0.2.1

Bug fixes

Patch for macOS. On macOS, assignment of nested lists is handled a bit differently than on other platforms. For instance, if first <- list(), then assigning first$second[[["third"]] <- 1 returns on Windows (and other platforms) a list named first, that contains another list named second, that contains a named element third equal to an unnamed length 1 numerical vector. On macOS though, it returns a list named first, that contains a named element second equal to a named (third) length 1 numerical vector. So second is a list on the other platforms, while being a named numerical vector on macOS. This caused a bug on macOS while computing standard errors.

API change by making use of S3 classes and methods:
- Replaced StateSpaceFit() for statespacer().
- Replaced StateSpaceEval(...) for statespacer(..., fit = FALSE).
- statespacer() returns a list object of class statespacer.
- Replaced StateSpaceForecast() for the S3 method predict.statespacer().

Major:
- Calculation of loglikelihood now done using c++. Major performance improvement as the loglikelihood potentially gets calculated a lot of times by the optimisation procedure.
Minor:
- Making use of crossprod and tcrossprod.
- Improved efficiency of the computation of standard_errors.
- y_temp outside of LogLikelihood function.
- Easier to find proper initial values, reducing time spent on trial and error by the user.