Add support for printing out generated source from transformations

[willemneal]

E.g. adding //@as-pect out at the top of the file writes out the generated source of the transformations made by as-pect.

[jtenner]

Okay. Since aspect creates multiple tests, and the transforms exist across every single file, how should we handle this?

// @as-pect out = [name].out.ts

I feel like we should give the user the ability to say "Whenever this file is transformed, output it in this location."

I am open to suggestions.