Prior to this change the `ipld-dag-cbor` and `ipld-dag-pb` modules
are re-exported so that can be accessed within the Browser bundle.
Those modules normally don't need to be used directly, they are
kind of implementation details of IPLD. Hence remove them.

BREAKING CHANGE: remove `types.dagCBOR` and `types.dagPB` from public API

If you need the `ipld-dag-cbor` or `ipld-dag-pb` module in the Browser,
you need to bundle them yourself.

No further changes are needed as js-ipfs-api is getting the raw blocks
from IPFS and does the whole parsing client-sided in JavaScript.

BREAKING CHANGE: dag-cbor nodes now represent links as CID objects

The API for [dag-cbor](https://github.com/ipld/js-ipld-dag-cbor) changed.
Links are no longer represented as JSON objects (`{"/": "base-encoded-cid"}`,
but as [CID objects](https://github.com/ipld/js-cid). `ipfs.dag.get()` and
now always return links as CID objects. `ipfs.dag.put()` also expects links
to be represented as CID objects. The old-style JSON objects representation
is still supported, but deprecated.

Prior to this change:

```js
const cid = new CID('QmXed8RihWcWFXRRmfSRG9yFjEbXNxu1bDwgCFAN8Dxcq5')
// Link as JSON object representation
const putCid = await ipfs.dag.put({link: {'/': cid.toBaseEncodedString()}})
const result = await ipfs.dag.get(putCid)
console.log(result.value)

```

Output:

```js
{ link:
   { '/':
      <Buffer 12 20 8a…> } }
```

Now:

```js
const cid = new CID('QmXed8RihWcWFXRRmfSRG9yFjEbXNxu1bDwgCFAN8Dxcq5')
// Link as CID object
const putCid = await ipfs.dag.put({link: cid})
const result = await ipfs.dag.get(putCid)
console.log(result.value)
```

Output:

```js
{ link:
   CID {
     codec: 'dag-pb',
     version: 0,
     multihash:
      <Buffer 12 20 8a…> } }
```

See ipld/ipld#44 for more information on why this
change was made.