Support locking OS thread
Support locking each I/O event-loop goroutine to an OS thread
About this change
Add functional option
LockOSThread used to determine whether each I/O event-loop is associated to an OS thread, it is useful when you need some kind of mechanisms like thread local storage,
or invoke certain C libraries (such as graphics lib: GLib) that require thread-level manipulation via cgo, or want all I/O event-loops to actually run in parallel for a potential higher performance.