removed unused methods(BeginPlay, Tick) and added rider plugin

Plugins/Developer/RiderLink/Source/RD/thirdparty/countdownlatch/README.md

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+CountdownLatch for C++ multi-threaded programming
+================================================
+
+**CountdownLatch in C++**
+
+-----------------------
+countdownlatch is a C++ library providing similar functionalities as availble with standard Java
+CountdownLatch class. It's main usage is: it allows one or more threads to wait until a set of
+operations being performed on other threads completes.
+
+
+**Below is an example regarding how to use the library**
+
+---
+
+```c++
+#include <unistd.h>
+#include <thread>
+#include <vector>
+#include <iostream>
+#include <countdownlatch.hpp>
+
+void fun(clatch::countdownlatch *cl) {
+    cl->await();
+    std::cout << "Wait is over " << std::endl;
+}
+
+int main() {
+    auto cl = new clatch::countdownlatch(10);
+    int i = 0;
+    std::vector<std::thread*> ts;
+    while (i++ < 2) {
+        std::thread *t  = new std::thread(fun, cl);
+        ts.push_back(t);
+    }
+
+    i = 0;
+    while (i++ < 10) {
+        sleep(1);
+        cl->count_down();
+    }
+    i = 0;
+    while (i < 2) {
+        ts[i++]->join();
+    }
+    i = 0;
+    while (i < 2) {
+        delete ts[i++];
+    }
+    delete cl;
+    return 0;
+}
+
+```