A utility to merge different values for entries of a same key to a single entry
greek-namedays uses a raw file to parse the name days data. This file contains duplicate keys (because it is just an extract from a database). Example:
"18/01": "Αθανάσιος",
...
"18/01": "Νικόλαος",
The desired behavior is to definitely have a single key with all the possible key values as a value (list of Strings):
...
"18/01": "Αθανάσιος, Νικόλαος",
...
mergevaluesforkey comes to the rescue.