Add ReadHistoryRecords() API to download the aggregate history
from the CH database. Requires a credential (possibly delegated) with the "readhistory" privilege. ReadHistoryRecords(credential, int index, int count); where index and count are optional, but to be useful you will want to track the index and ask for "count" records at a time until you get back an error saying there are no more to give you. You are limited to max 100 (the default is 10) time at a time. The return value is a list of records, where each record is an array of the data in the aggregate_history table and the manifest. There might be multiple records if the slice was updated, since there will be multiple manifests. I won't describe it, you can just print out a record and see it, it is all pretty obvious.