ErlendNilsen/OpenPop_Integrated_DistSamp: Ptarmigan IDSM v2.1

This release includes a range of changes and extension to multi-area workflows and documentation:

• An additional workflow setup that is invoked from terminal and uses Nix shell and GNUparallel
• Vignettes documenting multi-area and simulated data workflows with R/targets and Nix/GNUparallel
• A slightly altered model structure that uses first-year recruitment rate to parameterise initial juvenile densities
• Summarising of density across line transects within model to reduce memory load of the output
• A new definition-time if-else that allows leaving out telemetry data
• New function for calculating and visualizing sampling correlations between survival and recruitment
• New function for calculating and visualizing two measures of generation time
• Several updates to existing plotting functions

Single-area workflows can be run analogous to the multi-area workflows. The simulated data workflows are still functional, but they rely on the original setup from the v1.5 release.