feature: view core modules documentation

[tillre]

[rf]

There's actually this: https://github.com/trentm/nodedoc which does just that, but imo a more permanent solution is needed.

I definitely do want to do this. The problem is: node doesn't drop the markdown files anywhere when make installed (and even if it did, I can't rely on package maintainers leaving them where they are). So, I have to find a way to obtain the documentation for the version of node the user is running.

[rf]

I wrote a really simple implementation that just pulls the docs from node's master branch using raw.github.com, but I'm going to keep this ticket open while looking for a better solution.

[StreetStrider]

nodedoc scares me, since it's not an actual JS package, it's a python package where npm is used as a transport. The utility is good, though, but it would be better to have similar utility in JS world, written in JS.