This is fairly ugly and I think I'll need to mess around with the
feature configuration a while until we get something that's pleasant
to develop with. This still seems like a good idea, though, since
we _will_ need to be executor-agnostic in the end, or we'll have no
way to handle wasm or embedded environments.
Later down the road, we'll probably want to use futures::Executor or
futures::Spawn more than having global entry points in
tor_rtcompat. That would probably make our feature story simpler.
Tokio is the default now, since tokio seems to be more heavily used
for performance-critical stuff.
This patch breaks tests; the next one will fix them, albeit
questionably.
This adds two timeouts in total: one for sending begin, and getting
headers, and one for getting the rest of the data.
These timeouts are way too long right now, but at least the code is
there.
Nick Mathewson