Implementation for usleep

Implement `usleep` for Windows OS.

sqlite3_usleep_windows.go

@@ -0,0 +1,39 @@
+// +build cgo
+
+// Copyright (C) 2018 G.J.R. Timmer <gjr.timmer@gmail.com>.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file.
+
+package sqlite3
+
+// usleep is a function available on *nix based systems.
+// This function is not present in Windows.
+// Windows has a sleep function but this works with seconds
+// and not with microseconds as usleep.
+//
+// This code should improve performance on windows because
+// without the presence of usleep SQLite waits 1 second.
+//
+// Source: https://stackoverflow.com/questions/5801813/c-usleep-is-obsolete-workarounds-for-windows-mingw?utm_medium=organic&utm_source=google_rich_qa&utm_campaign=google_rich_qa
+
+/*
+#include <windows.h>
+
+void usleep(__int64 usec)
+{
+    HANDLE timer;
+    LARGE_INTEGER ft;
+
+	// Convert to 100 nanosecond interval, negative value indicates relative time
+    ft.QuadPart = -(10*usec);
+
+    timer = CreateWaitableTimer(NULL, TRUE, NULL);
+    SetWaitableTimer(timer, &ft, 0, NULL, NULL, 0);
+    WaitForSingleObject(timer, INFINITE);
+    CloseHandle(timer);
+}
+*/
+import "C"
+
+// EOF