20-45% speedup

OLD:
2.2-2.4K samples/sec
105 full GCs

NEW:
2.9-3.2K samples/sec
36 full GCs
minor fix

as per
https://typescript.codeplex.com/wikipage?title=Writing%20Definition%20%28.d.ts%29%20Files
await optimisations (WIP)

no longer creates a new promise on each await