Support chaining commands on CLI

[donmccurdy]

gltf-transform \
  [ prune ] \
  [ atlas --size 1024 ] \
  [ ao --samples 500 ]

https://github.com/SamVerschueren/listr

[donmccurdy]

this could make sense for the core library too...

container
  .transform(ao({samples: 100}))
  .transform(atlas({resolution: 256}));

container.pipe(
  ao({samples: 100}),
  atlas({resolution: 256})
);

[donmccurdy]

container.transform(...) is will work. I don't feel inclined to ditch Caporal for the CLI, and it doesn't seem to have an easy way to support chaining, so no CLI chaining for now.

[donmccurdy]

Idea for doing this with Caporal would be to use a pseudo-command syntax:

gltf-transform a+b+c in.glb out.glb

All commands would use default options. Detecting this when the CLI program starts we can dynamically inject the new compound command.

[donmccurdy]

Alternatively... maybe a new uber-command that does an appropriate full pipeline for you, with a few options but not necessarily everything. Chaining is kind of less necessary with the proposal for #791 anyway.