rewrite the client in typescript

[rmorshea]

closes: #743

Checklist

Please update this checklist as you complete each item:

• Tests have been included for all bug fixes or added functionality.
• The changelog.rst has been updated with any significant changes.
• GitHub Issues which may be closed by this Pull Request have been linked.

[rmorshea]

Note to self - see these articles for details on how to distribute ts code for general consumption:

• https://cameronnokes.com/blog/the-30-second-guide-to-publishing-a-typescript-package-to-npm/
• https://dev.to/remshams/rolling-up-a-multi-module-system-esm-cjs-compatible-npm-library-with-typescript-and-babel-3gjg

[Archmonger]

This might also be a good time to add in ES6 classes. Having a bunch of raw functions makes things harder to read.

[rmorshea]

Yup. I'm using all the modern features here. Hoping this will be easier to contribute to moving forward after these changes.