Rcpp models

[seabbs]

For compute-intensive analysis, R based models are often inadequate. A common approach for working around this is to implement the model in C and to then integrate it into other code using Rcpp.

idmodelr should include examples of Rcpp models that can be compared to their R versions. This should be a great help to those new to Rcpp.

Describe the solution you'd like
Replicas of all currently implemented models using Rcpp.

Additional context
All Rcpp models should work with all other package functionality.