Gracefully handle unsupported WOFF2 parsing

[yne]

Description

WOFF2 is becoming more and more popular and is now the default font format in font.google.com

So Opentype.js is more and more expected to parse and generate WOFF2.

However WOFF2 compression (as WASM) would bloat the opentype.js dist file by ~1400 KB.

A more modular approach would be to let the end-user do the WOFF compress/decompress wrapping if they need it.

Motivation and Context

This PR aim to solve this lack of support by pointing the user to a wrapping example if they try the directly load a WOFF2 file into opentype.js

How Has This Been Tested?

By loading a WOFF2 into opentype.js without decompresing it beforehand and looking at the reason given by the trown exception.

Screenshots (if appropriate):

[herrstrietzel]

@yne : Thank you so much for depicting this woff2 workaround – that's kind of a game changer!
First of all, this solution should be at least mentioned in the current documentation.
(I've discovered this approach rather by accident.)

In the long run, it might be better to include the admittedly complex brotli decompression by default – albeit I always appreciated opentype.js approach to keep the core as compact as possible.

Highly subjective: I think font parsing is rather a niche for creating graphics based on fonts.
You rarely need to include opentype.js as a mandatory script asset (like other front end libraries).
My point: the additional increase in file size might be negligible in favor of woff2 support.

[Connum]

This has been discussed before. Brotli decompression will not be integrated into opentype.js, but we do show a console message with a link to a description when trying to load a woff2 file.