Automagically determine rewrite paths

[novemberborn]

It should be possible to resolve the TypeScript configuration (including extended configurations) to determine what source directories are output where. That way, users won't have to configure the rewrite paths.

I'm not sure if TypeScript supports multiple configuration files within a project. Babel does, but AVA's Babel support ignores such configuration files. It'll be simplest to do the same here.

This means we'll assume the nearest TypeScript configuration file is in the project directory itself.

[cinderblock]

While it does automatically crawl the entire tree to find a tsconfig.json file, it will stop at the first one it finds.

However, TypeScript configuration does support "extending" another config file.