Replace buffer implementation with standard Uint8Array

The conditional use of node’s Buffer versus a shim based on Uint8Array leads to subtle incompatibilities between node and the browser. I just spent a couple hours debugging an issue in mapbox-gl-js that stems from the following difference:

var Pbf = require('pbf');
var pbf = new Pbf();
pbf.writeVarint(0);
console.log(pbf.finish().buffer.byteLength);

In the browser, this prints 16, as expected. In node, it prints 8192.

To eliminate this gotcha, pbf should use standard Uint8Array’s everywhere, and drop usage of Buffer.

[jfirebaugh]

I still think we should just use and accept the performance of Uint8Array. High-performance node applications are going to want to use a native module for pbfs anyway.

The current code forces copying the data in the browser when you do new Pbf(uint8Array).

[mourner]

Working on this. Managed to get the Uint8Array decoding perf drop to ~9% from ~46%.