Add system::sleep().

include/system.hpp

@@ -171,6 +171,7 @@ double getTime();
 */
 double getUnixTime();
 double getThreadTime();
+void sleep(double time);
 std::string getOperatingSystemInfo();
 
 // Applications

src/system.cpp

@@ -809,6 +809,11 @@ double getThreadTime() {
 }
 
 
+void sleep(double time) {
+	std::this_thread::sleep_for(std::chrono::duration<double>(time));
+}
+
+
 std::string getOperatingSystemInfo() {
 #if defined ARCH_LIN
 	struct utsname u;