cleanup & modernization

[sachaw]

A while ago, I attempted a refactoring of this library in: https://github.com/sachaw/micro-web-flasher However I have seen the recent effort in the typescript migration, I thought I'd focus my efforts here.

This will stay a draft PR until I'm happy with the state and have addressed any of the other developers concerns.

I hope this effort can bring the library more inline with current practices and be a major boost in maintainability.

[balloob]

Big PRs like this have very little chance of getting merged. If you want to do cleanups, please open PRs that address single issues.