Fixes #123

Replaces node buffers with browser-friendly `Uint8Array`s.

Previously we didn't want to do this because there's no equivalent
to node's `Buffer.allocUnsafe` which doesn't set all entries of
allocated buffers to 0.  The thing is we only actually use that in one
place so to address this I've isolated the use of `Buffer.allocUnsafe`
to the `alloc-unsafe.ts` file and used the `browser` field in package.json
to override it for browser use.

Running the benchmark suite in this module shows the performance
is comparable to or even slightly better than master (I think due to not
having to convert `Uint8Array`s to `Buffer`s any more):

Before:

```console
$ node benchmark.js
handshake x 59.95 ops/sec ±11.20% (75 runs sampled)
handshake x 54.68 ops/sec ±10.81% (68 runs sampled)
handshake x 50.42 ops/sec ±11.55% (65 runs sampled)
handshake x 53.41 ops/sec ±11.84% (68 runs sampled)
handshake x 50.25 ops/sec ±11.80% (66 runs sampled)
```

After:

```console
$ node ./benchmark.js
Initializing handshake benchmark
Init complete, running benchmark
handshake x 61.48 ops/sec ±11.71% (76 runs sampled)
handshake x 59.43 ops/sec ±11.13% (73 runs sampled)
handshake x 56.09 ops/sec ±12.02% (71 runs sampled)
handshake x 60.05 ops/sec ±11.69% (74 runs sampled)
handshake x 59.66 ops/sec ±10.59% (74 runs sampled)
```

Fix API docs link

fix: remove node buffers

fix: safely handle nonces as 64 bit uints

chore: bump version