gistfile1.txt

I think we're likely to want more options here in the future, but we should leave them for later.

I don't think we should add full 'do what you want with stderr' or even 'split stderr to another FD', but perhaps:
`foo($command, vec[$args], SubProcess\DISCARD_STDERR)`

A `shape('discard_stderr' => true)` approach instead would give us more flexibility in the future without either:
- using int flags that can't be fully understood by the typechecker
- growing the function signature

I think for the most common case, minimizing the surface area is important.