We now depend on libsodium unconditionally. Future work will require
functions from libsodium, and nobody we're aware of uses the nacl build
for anything other than making sure it still works on CI.
It doesn't work at all, because we're missing something in the net code
to do with endian conversions. I haven't investigated, yet, but at least
now we have a failing test that can be investigated.
Also moved to cmake 3.5 at minimum. CMake will stop supporting lower
versions than that, soon.
Also moved to C11 from C99 to get `static_assert`.
Also made a network ERROR into a WARNING. It triggers on FreeBSD.
