Merges the contacts specified into a single contact, deleting the merged-in contacts.
If a target contact ID is supplied, the other contacts will be merged into that one.
Otherwise, some contact in the contact ID list will be treated as the target contact.
Merge conflicts will be resolved in the following ways:
name will prioritize manually-updated and non-private contact names
descriptions will be concatenated and separated by newlines in order from
oldest to newest with the (optional) target contact's description first
all handles, groups, links, and notes will be preserved
other conflicts will use the most recently updated contact's value