Replace Boost.Asio with standalone Asio library

We had to add an even hackier hack now to get Boost.Process to
interoperate with Asio's IO contexts. This will be replaced later when
we replace Boost.Process.

src/plugin/bridges/vst3-impls/plug-view-proxy.h

@@ -32,7 +32,7 @@ class RunLoopTasks : public Steinberg::Linux::IEventHandler {
    public:
     /**
      * Register an event handler in the host's run loop so we can schedule tasks
-     * to be run from there. This works very much like how we use Boost.Asio IO
+     * to be run from there. This works very much like how we use Asio IO
      * contexts everywhere else to run functions on other threads. All of this
      * is backed by a dummy Unix domain socket, although REAPER will call the
      * event handler regardless of whether the file descriptor is ready or not.