Consider changing default `target` to ES5

[RyanCavanaugh]

ES3 runtimes are increasingly few and far between, and many common features (getters and setters, spread in new) only work in ES5. The 2.0 release would be a good time to take a BC break to update the default target to ES5.

Related, and somewhat confusingly, we emit a tsconfig.json with target: ES5 when running tsc --init even though the actual default target is ES3. We should at least be consistent here.

[unional]

One small counter argument. When I first get my hand on TypeScript, it is the ability to transpile down to ES3 that gets me to choose TypeScript over ES6 with Babel.

Of course things changed since then and more and more features are added.

So my personal opinion on this is mixed and neutral. 🌷

[RyanCavanaugh]

We'd still allow ES3 as a target, just not have it be the default.

[unional]

Oh. I thought we are dropping ES3. XD

All for it then. :)

[RyanCavanaugh]

👍 for TS 2.1. THE FUTURE IS NOW (eventually)