libp2p-host doesn't build

[faddat]

There are two possiblities here and I haven't investigated yet-- the first is that the example app is a very bare example and won't build till fleshed out. The second is that I've found a bug or some breakage from code churn. I'm not certain which it is and need to head to sleep, so figured I would post it regardless.

[Stebalien]

TL;DR: Run make deps in the root of the repository and try again.

We're working on pulling through some breaking changes so things are a bit broken at the moment if you use go get for dep management. This is why we use a tool we made called gx as our canonical dependency manger. It uses content addressing to address the dependencies (really, it just stores the deps in IPFS) so it tends not to have issues like this.

If you're wondering how this relates to the solution above, make deps will:

1. Install gx using go get.
2. Fetch the dependencies using gx.
3. Rewrite the dependencies in the go code to point to the dependencies fetched through gx.

---

In the future, we'd like to make it possible to fetch deps managed by gx using go get so everything "just works" (you'll never end up with the wrong dependency versions). We've (well, @lgierth and @whyrusleeping) recently figured out a way to do this that we think will work but have yet to implement it.