feature: get multiaddrs by capability

[daviddias]

https://github.com/diasdavid/js-peer-info/blob/master/src/index.js#L62-L63

It would be super cool™ to be able to get the multiaddrs by their capabilities, e.g:

• get all the multiaddrs that are on the tcp protocol
• get all the multiaddrs that use uTP and that are IPv6 addrs

https://github.com/whyrusleeping/js-mafmt can be used to achieve this

[daviddias]

added with #63