Remove JS files from repo & add npm prepublish script

[Bartvds]

The compiled JavaScript doesn't have to be checked-in, but instead be compiled before packaging in a prepublish script via package.json. It runs automatically when running npm publish.

Saves a lot of noise in the diffs, I use it in all my TS projects.

[nexussays]

Agreed. Very annoying to commit what amount to build artifacts.