Added ipuz as development requirement as it's one of the features this package needs to support
Added test to clarify default ordering of clues
Modified logic for clues to keep track of order in which they were inserted (by default)
Added ability to sort clues using a specified function
Updated all() method to use the sorted order of the underlying CrosswordDirectionClues objects
flake8 cleanup of tests
Make sorting clues in numerical order the default. Other sorting options are possible via sort function