Rename link to socket, move from ssu to uia::comm. Move endpoint.
Update docs.
Move files to the right directory corresponding to the namespace.
Rename link_channel to socket_channel.
Split off headers for key_initiator and key_host_state.
Code formatting cleanup.
Move platform code for sockets to comm.
Comment clean up.
Use simulator_fixture to remove boilerplate from tests.
Remove unused header.
Split off implementation code for socket_host_state and socket_receiver.