contact/edit - Edits an existing contact.

Method parameters:
id - The ID of the contact to edit.
full_name - The new full name of the contact.
alias - The new alias of the contact.
address - The new address of the contact.
email1 - The new primary email of the contact.
email1_label - The new label of the primary email of the contact.
email2 - The new secondary email of the contact.
email2_label - The new label of the secondary email of the contact.
phone1 - The new primary phone number of the contact.
phone1_label - The new label of the primary phone number of the contact.
phone2 - The new secondary phone number of the contact.
phone2_label - The new label of the secondary phone number of the contact.
birthday_time - The new Unix timestamp of the birthday of the contact.
username - The new Zvini username of the contact.
timezone - The new timezone offset of the contact in minutes.
tags - A space-separated list of tags.
notes - Additional notes of the contact.
favorite - Whether the contact should be marked as favorite.

Returns a JSON document of the following format:
<boolean> - Always true.

Expected errors:
CONTACT_NOT_FOUND - A contact with the ID doesn't exist.
ENTER_FULL_NAME - The new full name is empty.
TOO_MANY_TAGS - More than 5 tags given.