Convert this repo into an example builder

[vorg]

Collect all the examples from various repos e.g. pex-context/examples and pex-renderer/examples and pex-gltf/examples

[vorg]

What this repo could provide:

• copy the examples
• check if they have npm build scripts
• build them
• takes screenshots
• check lib versions
• output some json or html for a pex.gl website etc