Publish to npm

[jtpio]

The package should be published to npm, so it can used on a local machine too.

It can also be made compatible with npx, so that running npx p5-notebook (or npx p5nb) starts a server in the local directory and open a new browser tab. It should also serve other type of content such as images.

[jtpio]

This should be automated with a GitHub Action workflow.