make it possible to publish Positron to NPM

[mykmelez]

We should make it possible to publish Positron to NPM so testers can start testing it with their own Electron apps. Right now it won't run most of those apps, so the NPM package won't be very useful. But it'll become more useful over time. And this work can be done in advance, so we have packages available the moment Positron becomes useful enough to advertise to a larger audience of testers.

There's already some code in the tree to make the the dist/ directory into an Node module, specifically the positron/package.json and positron/cli.js files (and the code in positron/Makefile.in to copy them to the appropriate place).

[jryans]

The "positron" package name is already taken (like nearly every imaginable word on npm), so you may have to use a scoped package like "@mozilla/positron".

[Ryuno-Ki]

Well, electron uses electron-prebuilt and positron-prebuilt is available.