Buffer usage elimination #1

[nazar-pc]

This is the first step in reducing bundle size as discussed in #280

This PR removes explicit usage of Buffer API in simple-peer itself, but Buffer is still used by debug and readable-stream, so bundle size will not be much smaller just yet, those will be tacked in a separate PR.

One major implication of this PR is that data event will dispatch with Uint8Array instead of Buffer, which is a major breaking change.

I believe this is a reasonable trade-off since It is easy to upgrade existing code base with Buffer.from(data), while browser users that don't need Buffer API will have significantly less code to download.

[feross]

While I sympathize with the desire to make the browser bundle smaller, the entire reason that I initially created this package was to expose the WebRTC data channel as a Node.js stream.

If we remove Buffer and eventually break the Node.js Stream interface, then it becomes impossible to use simple-peer with the huge ecosystem of other Node.js Stream packages, and it becomes impossible to use it as a drop-in substitute for a net.Socket object like we do in WebTorrent, and others do in other P2P applications.

I think we may need to consider how to satisfy these two use cases in some other way. I'll think about it some more and share possible ideas in the original issue #280.

[mrlika]

I also disappointed that huge Buffer is used everywhere. Bundles for the browser should be small. Changing the code to use compatible between Node.js and browsers ArrayBuffer/Uint8Array is the way to go.