Performance issue

[kuanyui]

First, thanks for your project. This library is fabulous for TypeScript as a robust strong-typed event emitter, I doesn't find any other library can do this so well.

However, I found the performance is an issue which cannot be neglected in this library. I profile some EventEmitter libraries:

const Benchmark = require('benchmark')
const EETS = require('ee-ts/lib/ee').EventEmitter
const EE3 = require('eventemitter3')
const FE = require("@foxify/events").default

let TMP = ''
function dummyFn(x) {
  TMP = x
}

class KlsOnXXX {
  run() {
    this.onHello('hello')
  }
}

class KlsEETS extends EETS {
  run() {
    this.emit('hello', 'hello')
  }
}
class KlsEE3 extends EE3 {
  run () {
    this.emit('hello', 'hello')
  }
}
class KlsFE extends FE {
  run () {
    this.emit('hello', 'hello')
  }
}

const kls_onxxx = new KlsOnXXX()
const kls_eets = new KlsEETS()
const kls_ee3 = new KlsEE3()
const kls_fe = new KlsFE()

kls_onxxx.onHello = function (ev) { dummyFn(ev) }
kls_eets.on('hello', function (ev) { dummyFn(ev) }  )
kls_ee3.on('hello', function (ev) { dummyFn(ev) }  )
kls_fe.on('hello', function (ev) { dummyFn(ev) }  )

var suite = new Benchmark.Suite
suite
.add('onXXX', function () {
  kls_onxxx.run()
})
.add('ee-ts', function () {
  kls_eets.run()
})
.add('ee3', function () {
  kls_ee3.run()
})
.add('fe', function () {
  kls_fe.run()
})
.on('cycle', function(event) {
  console.log(String(event.target));
})
.on('complete', function() {
  console.log('Fastest is ' + this.filter('fastest').map('name'));
})
.run({
  'async': false, // https://benchmarkjs.com/docs#options_async
  'delay': 1
});

And the result is astonishing...

onXXX x      193,150,752 ops/sec ±4.00% (88 runs sampled)
ee-ts x        1,732,183 ops/sec ±3.64% (77 runs sampled)
ee3 x         52,713,790 ops/sec ±1.11% (89 runs sampled)
fe x         122,749,677 ops/sec ±0.55% (89 runs sampled)
Fastest is onXXX