Low browsers support

[Semigradsky]

Describe the bug
Currently, private methods are used in code. By CanIUse data only 84.6% of users on desktop and 77.66% users on mobile have the support of this feature.

As was mentioned on #19 (comment) it is needed to transpile framework code or smth like this.

Expected behavior
At least 94% of browsers support.

Additional context

[rohiievych]

We can separate sources from transpiled code in folders src and lib or lib and dist.
Then transpile on publish and ship only transpiled version:

{
  "main": "lib/index.js",
  "scripts": {
    "prepublish": "babel src --out-dir lib"
  },
  "babel": {
    "presets": ["es2015"]
  }
}