Add Deno support

## Summary

This probably would take way too much time, but [Deno](https://deno.land/) is a simple, modern and secure runtime for JavaScript, TypeScript, and WebAssembly that uses V8 and is built in Rust and I would like that brain.js would be ported to Deno without [a CDN](https://cdn.esm.sh/brain.js) and [compatibility mode](https://deno.land/manual/node/compatibility_mode).

### Basic example

```ts
import brain from 'https://deno.land/x/brainjs/mod.[ts/js]'

// provide optional config object (or undefined). Defaults shown.
const config = {
binaryThresh: 0.5,
hiddenLayers: [3], // array of ints for the sizes of the hidden layers in the network
activation: 'sigmoid', // supported activation types: ['sigmoid', 'relu', 'leaky-relu', 'tanh'],
leakyReluAlpha: 0.01, // supported for activation type 'leaky-relu'
};

// create a simple feed forward neural network with backpropagation
const net = new brain.NeuralNetwork(config);

net.train([
{ input: [0, 0], output: [0] },
{ input: [0, 1], output: [1] },
{ input: [1, 0], output: [1] },
{ input: [1, 1], output: [0] },
]);

const output = net.run([1, 0]); // [0.987]
```

### Motivation

To add support for Deno so developers that use Deno can use this library easier.