Converts a step name of the form "step_YEAR_SEASON" or
"YEAR_SEASON" (as returned by simmar) into a named
list containing the clean year-season string, the integer year, the integer
season, and the decimal year used in process_marlin output.
Value
A named list with:
year_seasonCharacter. Clean
"year_season"string (any"step_"prefix removed).yearInteger. The year component.
seasonInteger. The season component.