Based on the API discussion yesterday, this removes the typescript_internal.d.ts and only uses the @internal comment to remove no public APIs.

I have marked everything we did not talk about as internal for now. the only changes I have made is exposing:

• getPreEmitDiagnostics -- used in one of the samples already
• parseCommandLine -- references in issue v1.5.0-alpha hides parseCommandLine #2620

Tip: look at bin\typescript.d.ts to see what changed in the public API surface area.