Issue/137 add entry point index js

[programarivm]

All examples have been tested using the new entry point and now some are importing cm-chessboard files from index.js. Closes #137

[programarivm]

Also by the way the package.json file could be updated as shown in chesslablab/cmblab in order to define the primary entry point of the library.

...

  "module": "./src/index.js",
  "browser": "./src/index.js",

...

However, if doing so I'm not too sure about how this would be backward-compatible with previous versions.

import {
  Chessboard,
  BORDER_TYPE,
  FEN
} from 'shaack/cm-chessboard'

[shaack]

I understand that this is your style of doing imports, but I prefer importing from the original files. Maybe because I am from Java and want to keep it simple. For importing the classes from node_modules or somewhere else, I use importmap. https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script/type/importmap

<script type="importmap">
    {
        "imports": {
            "cm-chessboard/": "./node_modules/cm-chessboard/"
        }
    }
</script>

With defining the module path in importmap (like above) you can import like this

import {Chessboard, COLOR, INPUT_EVENT_TYPE} from "cm-chessboard/src/Chessboard.js"

What is the reason that you want to put everything in an index.js? This file must also be maintained for changes such as refactoring.

[programarivm]

See #137 (comment)