Publish latest on npm / enable installing from repo

[strazzere]

Thanks for all the great work on the conversion to typescript - this actually cleared up many things on my side.

Was wondering if we could get a push to the npm repository of the latest, at there seems to be a version/code mismatch.

I can submit a PR for the following changes as well;

strazzere@1939df6

Though essentially I added rollup back as a dev dependency, added it to the build command since the main entry point in the package.json has no was to be created. Then I added the prepare script which allows a user to do a direct npm install https://github.com/theuser/therepo.

[amartinz]

/cc @Flohack74 @mariogrip @NeoTheThird