Renamed folders for consistency, using sim/athena/shared schema (#27)

Rename the following folders:
hal/lib/Athena -> hal/lib/athena
hal/lib/Desktop -> hal/lib/sim
hal/lib/Shared -> hal/lib/shared
wpilibc/Athena -> wpilibc/athena
wpilibc/simulation -> wpilibc/sim

Windows users may need to run gradlew clean after updating.

hal/lib/athena/cpp/Semaphore.cpp

@@ -0,0 +1,32 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2015-2016. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "HAL/cpp/Semaphore.hpp"
+
+Semaphore::Semaphore(uint32_t count) { m_count = count; }
+
+void Semaphore::give() {
+  std::lock_guard<priority_mutex> lock(m_mutex);
+  ++m_count;
+  m_condition.notify_one();
+}
+
+void Semaphore::take() {
+  std::unique_lock<priority_mutex> lock(m_mutex);
+  m_condition.wait(lock, [this] { return m_count; });
+  --m_count;
+}
+
+bool Semaphore::tryTake() {
+  std::lock_guard<priority_mutex> lock(m_mutex);
+  if (m_count) {
+    --m_count;
+    return true;
+  } else {
+    return false;
+  }
+}