Add unit tests, fix deno + TS strangeness

[yellowsink]

Adds unit testing via mocha and an action.

npm i
npm test

Make sure to rebuild via prepublish before testing.

Also fixes Deno "fixes" that broke typescript on everything else.
I suggest instead of using the deno.land/x CDN to use cdn.esm.sh,
which can simply bundle & minify the dist/esm from the npm package.

- typescript fixing
- add unit tests
- add actions CI