IPFS API design

[chunningham]

The currently accessible IPFS API is very limited and has missing features:

• only get, put and delete for single blocks at a time
• no built-in pinset replication/synchronisation
• the codec param is unused, all blocks are encoded as raw binary, disallowing pinning of full DAGs.

This API should at least:

• allow invoker-decidable block encodings based on the codec param (or similar)
• replicate the pin set based on puts and deletes

and preferably also enable the insertion of downstream DAG blocks when inserting/pinning a root block.