Exclude 'external' typings (such as node.d.ts) by default, fixed hang bug, and more

Hi Bart,

It's become a more extensive change than I had imagined at first, but here it is.

Note that I have changed the default behavior to (hopefully) be more in line with 'generic' use, i.e. exclude external typings by default, don't delete source typings, etc.
These are the options you'd need to regain the 'old' behavior:

```js
dts.bundle({
	name: 'cool-project',
	main: 'build/index.d.ts',
	out: 'build/index.d.ts',
	includeExternal: true,
	deleteSourceTypings: true,
});
```

You may also find `verbose: true` to be useful :)

If you accept the pull, may I suggest you update the package version, and publish it?
Btw: because npm treats 0.x.x versions differently, I'd also suggest bumping to 1.x.x.

Grtz!
Martin