Without this feature, each bundle would have to create its own typings
template to include references to dependent typings. Now, the references
can be declared in JS, along with other meta information about the
bundle typings.
Closes#3540
This means that we can now run just the d.ts file generation by running:
```bash
gulp docs/typings
```
In addition the type definition generation was messing with the other docs tasks
so separating it also fixes problems there.
