Memory/RAM solutions

We'll need to think about how and "where" to deal with RAM limitations, when dealing with e.g. many climate projections.
At the moment, in a 32GB machine, `climr` runs out of memory if all GCMs/periods/scenarios are requested (`process_one_raster` runs out of memore when `extract`ing the climate values)

Options are to (not mututally exclusive):
1. (partially) deal with these in `climr`
2. deal with these externally to `climr` (e.g. in the modules that will need to extract cliamte projections)
3. have `climr` warn the user about memory limitations (implemented in `climr@out-of-memory-extract`)