WIP - cross browser usage with Rollup

[mrchrisadams]

🚨🚨🚨 this isn't close to being ready for merging 🚨🚨🚨

This is an experimental PR that instead of having fairly awkward to use build that largely assumes it's working in a nodejs runtime, instead provides:

• one pre-compiled web friendly build that you can include like a simple script
• one ES module build for use in applications
• one commonJS based build for continued use in nodejs

This uses Rollup, to create these builds, and the goal is for the first two builds not to have any code that assumes nodejs at all, but instead uses webby APIs like fetch instead.

[mrchrisadams]

Closing this, in favour of merging the new v0.10.0 work in, as it's much tidier, and the PRs merging into it should do a better job of explaining what changes have been made