Deploys on pull requests

[francoischalifour]

This PR sets the environment to enable previews on deploy when we send pull requests.

Why

medium-zoom is now hosted on Netlify. It would be nice to create previews for each pull request. It would avoid to pull the code locally and check that the new code works.

Problem

However, Netlify currently serves /examples/javascript as index. The javascript folder contains the default index.html which is the demo, development/index.html for development purpose and preview/index.html to preview a pull request (hopefully).

Since the /examples/javascript folder is not the root, we can't access /dist which contains all the built library. We therefore need to copy these files to /examples/javascript/preview before previewing the changes. Thus, the new script npm run preview.

Solution

In the javascript example:

• Create a local development environment
• Create a public preview environment which gets populated when Netlify triggers a deploy for pull requests (available at the route /preview)
• Add logs in the console in development and preview modes
• Add instructions in the README

To run on Netlify:

• Create a script npm run preview that builds the library and populates the preview environment

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Hopefully this will work and trigger a preview for each PR at [name].netlify.com/preview.