Update code style guidelines

[Eugeny]

I'm working on PuTTY key format support right now, and jsstyle is driving me nuts.

Are you open to replacing it with eslint? I'm not saying change your code style - just replicate the same rules in an eslint config.

jsstyle is:

• dead
• uses an ancient code parser and hence doesn't support syntax features such as spreads, shorthand fields, etc
• plain broken - line length limit is actually 75 even though it's reported as 80

Also do we really have to limit width to 25% of a modern display? I have to avoid descriptive function names now and shuffle line breaks around in a game of trying to pass jsstyle rules.

[bahamat]

We use jsstyle a ton of repos, so swapping out is not a light task. It's one of our significant legacy issues.

What I can do for you though, is if you've got a commit working, go ahead and submit it to us and I can work through making sure jsstyle passes.