Add rollup dev server

[texodus]

Rebased #39, and

• Merge rollup.config.js and rollup.dev.config.js into one file, whose behavior dispatches on the presence of the --watch flag.
• Deleted index.html root page, since this is no longer where examples live, and http-server has a directory listing built-in.
• Remove rollup-plugin-serve and replace with good old http-server
• Revert yarn changes and other pieces which are not applicable to remainging changeset