bookmark/edit - Edits an existing bookmark.

Method parameters:
id - The ID of the bookmark to edit.
url - The new URL of the bookmark.
title - The new title of the bookmark.
tags - A space-separated list of tags.

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

Expected errors:
BOOKMARK_NOT_FOUND - A bookmark with the ID doesn't exist.
ENTER_URL - The new URL is empty.
TOO_MANY_TAGS - More than 5 tags given.