feat: support v4 console access

[mattkhan]

Problem

The latest version (4.1.0 at the time of this PR) cannot be loaded in the console via init("v4.1.0")

Solution

Before: the unkpg url would be appended with /esm/index.js regardless of the version
After: if the version starts with 4, append /index.js instead

• same behavior for all versions that do not start with 4

Also defaults init() to use the current latest version.

Tested in Chrome locally

This should partially resolve #222

only partial because V3 is not supported

Alternatively, unpkg mentions:

If you omit the file path (i.e. use a “bare” URL), unpkg will serve the file specified by the unpkg field in package.json, or fall back to main.

[asselin]

@kossnocorp The website is a great resource to understand how the functions work. Currently only 2.x is loadable in the website, and there's been a considerable number of changes between 2.x and 4.x. Could you please merge this PR to make 4.x available for use in the website?

Thank you for this awesome library, and all your work over the years on it!