Provide a dedicated typescript typings file

[lukastaegert]

resolves #50

Even though this package had typings defined in its package.json file (that linked to the source folder), I never got these to work for me. This PR adopts the approach followed by Rollup that maintains a hand-crafted file for its external types that is used internally as well to ensure consistency. In my experiments, this now works very well.

Another advantage is that there no longer is a reason to publish the sources with the package. I still kept them in as removing them would be a breaking change but this is something I would recommend for the next major version.

Feedback welcome.

[eventualbuddha]

This is an interesting approach. I think a typings bundler--like what rollup does--would be a more ideal solution, but this does work without additional tooling.

[lukastaegert]

I think a typings bundler--like what rollup does--would be a more ideal solution

I was not actually aware that such tools existed but I stand corrected, though most of those tools describe themselves as "hacky". Will keep an eye on this. Unfortunately, none of them looks like they would support code-splitting how Rollup does it. That could become a really interesting addition to rollup-plugin-typescript.

[eventualbuddha]

I was not actually aware that such tools existed but I stand corrected, though most of those tools describe themselves as "hacky".

Yeah, I've come across a few but none seemed very good. I agree it would be great if rollup-plugin-typescript could just handle it.