rollcast 0.1.0

• Initial CRAN-ready package structure.
• Implements Rollcast probabilistic forecasting.
• Includes scalar-or-vector causal hyperparameter search.
• Includes Rcpp-accelerated conditional density and recursive prediction.
• Includes predictive density, CDF, quantile, and random-generation functions.
• Includes fan-chart and diagnostic plotting.
• Includes testthat tests and an introductory vignette.