[Docs] Document the DAG API (which uses IPLD)

[flyingzumwalt]

Explore the DAG API and write documentation for the Primer. See discussion in ipfs/specs#98

Also make sure to remove any reference to ipfs object in the Primer, since that uses protobuf objects, which are being deprecated.

If people have other reference info to offer, please let me know. cc @nicola @RichardLitt @diasdavid @whyrusleeping

Example Audience/Use Cases:

• OpenBazaar adding JSON info to IPFS as IPLD blocks on the DAG

Reference Info

• Unite the Files API 🗂 specs#98
• http://ipld.io

[daviddias]

Documentation: https://github.com/ipfs/interface-ipfs-core/tree/master/API/dag
Examples: https://github.com/ipfs/js-ipfs/tree/master/examples/dag

[daviddias]

//cc @vmx :)

[daviddias]

Documented https://github.com/ipfs/interface-ipfs-core/blob/master/SPEC/DAG.md, lots of design work happening on https://github.com/ipfs/interface-ipfs-core/issues/81