Tries to convert sentences by finding key in ruleset. If key not found then codes unknown.
@param row: The row to assign values to @param ruleset: The ruleset which stores the key, value rule mappings to convert a given key into sentence variables @param skip_unknown: A list of variables which should not be coded during unknown coding. @return: Returns the key that was passed in on key param. If remove_key is true will remove the key that was matched on from the string
alias of src.sentence_rules