auk_complete: Filter out incomplete checklists from the eBird data
Description
Define a filter for the eBird Basic Dataset (EBD) to only keep complete
checklists, i.e. those for which all birds seen or heard were recorded. These
checklists are the most valuable for scientific uses since they provide
presence and absence data.This function only defines the filter and, once all
filters have been defined, auk_filter() should be used to call AWK and
perform the filtering.