module Jekyll::Utils

def pluralized_array_from_hash(hash, singular_key, plural_key)

Returns an array

plural_key - the plural key
singular_key - the singular key
hash - the hash to read from

and then the plural key, and handling any nil entries.
Read array from the supplied hash favouring the singular key 
def pluralized_array_from_hash(hash, singular_key, plural_key)
  array = []
  value = value_from_singular_key(hash, singular_key)
  value ||= value_from_plural_key(hash, plural_key)
  array << value
  array.flatten!
  array.compact!
  array
end