Generic Modules/Utils

Before moving on to the rest of libp2p and py-ipfs, we should look at the required generic utilities and determine which existing implementation we want to use, or if there isn't one, who wants to work on it. Here is what we need (see https://github.com/ipfs/py-ipfs/issues/21#issuecomment-158019175 for more info):
- [ ] PeerID
- js impl: https://github.com/diasdavid/js-peer-id
- [ ] PeerInfo
- js impl: https://github.com/diasdavid/js-peer-info
- [X] multihash
- specs: https://github.com/jbenet/multihash
- go impl: https://github.com/jbenet/go-multihash
- js impl: https://github.com/jbenet/js-multihash
- py impl: https://github.com/ivilata/pymultihash
- [ ] multihashing (optional, `pymultihash` delegates this mostly to `hashlib`)
- specs: ???
- js impl: https://github.com/jbenet/js-multihashing
- [X] multiaddr
- specs: https://github.com/jbenet/multiaddr
- go impl: https://github.com/jbenet/go-multiaddr
- js impl: https://github.com/jbenet/js-multiaddr
- py impl: https://github.com/sbuss/py-multiaddr
- [ ] multistream
- specs: https://github.com/jbenet/multistream
- js impl: https://github.com/diasdavid/js-multistream
- [X] multicodec
- specs: https://github.com/jbenet/multicodec
- go impl: https://github.com/jbenet/go-multicodec
- py impl: https://github.com/multiformats/py-multicodec
- [X] ipld
- specs: ???
- discussion: https://github.com/ipfs/go-ipld/issues/8
- go impl: https://github.com/ipfs/go-ipld
- py impl: https://github.com/ipld/py-ipld-dag

I know we already have [several multihash implementations](https://github.com/ipfs/py-ipfs/issues/13), and I hacked together a [multiaddr implementation](https://github.com/amstocker/python-multiaddr) that could use some love. If anyone has already worked on any of these or is interested on working on any of them, please comment here. Also if anyone has anymore links to references or specs for the generic modules, post them here.