The dependencies `netservices`, `io-reactor` and `popol` served us well,
however they do not support Windows and are not actively maintained.
This change removes the aforementioned dependencies (and `libc` along
with them). It reuses the integration with `cyphernet` from
`netservices` for Noise and SOCKS.
The new module `reactor` is a rewrite of `io-reactor` on top of Mio.
Note that no tests were changed.
3c3d81a085