Renames all our .hpp HAL files to .h (#44)

Adds consistency, as the HAL was .hpp however all other code was .h.

hal/include/HAL/cpp/Semaphore.h

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <condition_variable>
+#include <cstdint>
+
+#include "HAL/cpp/priority_mutex.h"
+
+class Semaphore {
+ public:
+  explicit Semaphore(uint32_t count = 0);
+  Semaphore(Semaphore&&);
+  Semaphore& operator=(Semaphore&&);
+
+  void give();
+  void take();
+
+  // @return true if semaphore was locked successfully. false if not.
+  bool tryTake();
+
+  static const int32_t kNoWait = 0;
+  static const int32_t kWaitForever = -1;
+
+  static const uint32_t kEmpty = 0;
+  static const uint32_t kFull = 1;
+
+ private:
+  priority_mutex m_mutex;
+  std::condition_variable_any m_condition;
+  uint32_t m_count = 0;
+};