Release 1.0.0b26

Not a huge amount in this release, but a few noteworthy changes:

• The simplifier is now much faster at working out what names are free/bound in expressions (needed for closures and unused-let-elimination) – it turns out that this was a surprising performance drain.
• There are also a bunch of other minor performance tweaks to the simplifier.
• 3D primitives can be converted directly into manifold objects if that's what we need.
• Time-codes and symbols can be used on the command-line when defining static name bindings.
• The AGX tone-mapping function (plus the "punchy" variant) has been added to the !adjust node.
• @ingydotnet contributed a bunch of YAML fixes to the GitHub workflow files.
• A few documentation fixes.

Full Changelog: v1.0.0b25...v1.0.0b26