3. [CSCI 503 Only] Add Measure Filtering

For this part, you will update the port_entries.compare module and add the ability to filter by measure. Create a new function filter_by_measure that will filter the returned items from the diff methods to only include those that match the specified measure(s). (Note that this could be integrated when doing the comparisons, but please do this as post-processing for this assignment.) Then, update the command-line program so that a user can add an optional argument -m followed by an expression representing measures.