Add one build npm script. Add github actions CI

[romang-at-guarda-co]

This allows users to build everything like this:

npm ci
npm run build

And also adds a github workflow which runs these commands and npm run test afterwards to make sure this build works.

[devinpearson]

Thanks for the submission @romang-at-guarda-co

Ill have a look at it properly tomorrow. If you are interested in taking it further. Ive made a number of changes to our newer library that can be found here. https://github.com/mymonero/mymonero-utils/tree/master/packages/mymonero-monero-client and here: https://github.com/mymonero/mymonero-utils/tree/master/packages/mymonero-wallet-manager

The newer code is using boost headers and the latest emscripten docker image to do the builds. these would fit well with the changes you have made.

[romang-at-guarda-co]

Sorry, I think I'm interested in this repo specifically (I have legacy code that depends on it).

[devinpearson]

no problem. just suggesting that you can drop the downloading of boost and the need for a custom emscripten docker container. the code in this repo does work with the latest emscripten and boost headers.

[romang-at-guarda-co]

I think I got it.