Expand doctests

[drewcassidy]

I know this is an extremely niche thing to want, but the macro im working on fails in doctests where it succeeds in other code. Being able to expand the doctests would be very helpful to understand what is happening here (Ive tried: cargo expand --lib --tests doesnt include doctests. im guessing there's some hidden target I can point it at but my searches of the documentation turn up nothing)