sort_by_prop $prop, $records, $sort_undef_last

Given a property name and an arrayref to a list of records, returns a list of the records sorted by their "created" property, in ascending order.

If $sort_undef_last is true, records which don't have a property defined are sorted *after* all other records; otherwise, they are sorted before.

group_by_prop $prop => $records

Given a property name and an arrayref to a list of records, returns a reference to a list of hashes of the form:

    { label => $label,
      records => \@records }