Improvement/html demo

[erayalkis]

Description of change

Fixes #28, an issue caused by the HTML demo having no way of setting up a local server, resulting in any users that open the HTML file manually on their browser getting a CORS error.
The updated demo uses express.js to serve files through a local server, fixing the error and granting the users a simpler way to set up a local server.

Pull-Request Checklist

• Code is up-to-date with the main branch
• npm run lint passes with this change
• npm run test passes with this change
• This pull request links relevant issues as Fixes #0000
• There are new or updated unit tests validating the change
• Documentation has been updated to reflect this change
• The new commits follow conventions outlined in the conventional commit spec

[erayalkis]

Sidenote, this new PR still uses jsdelivr since other solutions would've required either a webpack or babel setup, and I didn't go with that option as I didn't want to bloat up the demo folder. If these solutions are necessary though, I can get on it ASAP 😄