Requires moving Atom rendering from DistributionWorker (where
`stream_entry.status` is already nil) to inline (where
`stream_entry.status.destroyed?` is true) and distributing that.
Unfortunately, such XML renderings can no longer be easily chained
together into one payload of n items.
* Add handling of Linked Data Signatures in payloads
* Add a way to sign JSON, fix canonicalization of signature options
* Fix signatureValue encoding, send out signed JSON when distributing
* Add missing security context
* Make Pubsubhubbub::DistributionWorker handle both single stream entry
arguments, as well as arrays of stream entries
* Add BatchedRemoveStatusService, make SuspendAccountService use it
* Improve method names
* Add test
* Add more tests
* Use PuSH payloads of 100 to have a clear mapping of
1000 input statuses -> 10 PuSH payloads
It was nice while it lasted
