* Code modernization: subfolders
Modernize various code on subfolders client, network, script, threading, unittests, util
* empty function
* default constructor/destructor
* for range-based loops
* use emplace_back instead of push_back
* C++ STL header style
* Make connection.cpp readable in a pointed place + typo
This unifies the settings APIs.
This also unifies the sync and async registration APIs, since the async
registration API did not support adding non-functions to the API table.