Function that translates park unit codes into full park names

[RobLBaker]

Many people use park unit codes in their dataset. These are largely unintelligible to people outside NPS (and even some of us inside NPS). A function that looks up the park unit code and returns the full park unit name would be useful. This would be particularly useful if it could be performed on an entire dataframe where the full park name is assigned to a new column in the dataframe.