We can't remove it otherwise we have object of type closure is not subsettable when running in parallel.

Models needs to be initialized since now we use models_list. Remove more variables and call garbage collector.

Avoid re-assignments to the same variable name so we can delete the content and help the garbage collector to clean memory.

When the user does not need to save the runs, then we should not build a complete Habitat Class object which takes a lot of space in memory.

The user can now specify the max number of cores. This helps us to control the ratio of available cores and main memory.

We do not use string NULL anymore to mark models which did not have high accuracy. Do the which only once and use vapply for vectorize processing.

First drafts for the documentation. The inner_procedure is not exported but all other functions are.