js: Adjust simplify/simplifyWithAttributes assertions

To make ErrorAbsolute mode useful in JS, it needs to allow values
outside of 0..1 range; for simplicity we just remove the upper bound for
now.

Also, previously flags could contain values that are not recognized as
valid options and this would silently work; these are now checked with
assertions to prevent mistakes.

Update version to 0.20

Merge pull request #554 from zeux/update-node

Update versions of setup-node and upload-artifact

Merge pull request #447 from zeux/nextver

Update version to 0.18 and copyright year to 2022

js: Update meshopt_encoder.module from NPM builds

Update README.md

The previous change missed one version number due to the use of "whole
word" string search.

gltfpack: Update npm version to 0.15.1

This is to fix the I/O issue with node.js and small files.

Update README.md

Mention meshopt_optimizeVertexCacheStrip and meshopt_encodeIndexVersion.

demo: Update to three.js r111

Cloudflare has r109 as the latest version, so switch to jsdelivr.

gltfpack: Fix bufferView alignment

Instead of aligning *after* the offset for a buffer view was computed,
we now align each chunk that is written to the binary. This makes sure
that the start of the next chunk as well as the entire resulting buffer
is 4b aligned.