Clean up threading

* Rename everything.
    * Strip J prefix.
    * Change UpperCamelCase functions to lowerCamelCase.
  * Remove global (!) semaphore count mutex on OSX.
  * Remove semaphore count getter (unused, unsafe, depended on internal
    API functions on Windows, and used a hack on OSX).
  * Add `Atomic<type>`.
  * Make `Thread` handle thread names.
  * Add support for C++11 multi-threading.
  * Combine pthread and win32 sources.
  * Remove `ThreadStarted` (unused, unneeded).
  * Move some includes from the headers to the sources.
  * Move all of `Event` into its header (allows inlining with no new includes).
  * Make `Event` use `Semaphore` (except on Windows).
  * Move some porting functions into `Thread`.
  * Integrate logging with `Thread`.
  * Add threading test.

src/script/cpp_api/s_base.h

@@ -28,8 +28,8 @@ extern "C" {
 }
 
 #include "irrlichttypes.h"
-#include "jthread/jmutex.h"
-#include "jthread/jmutexautolock.h"
+#include "threading/mutex.h"
+#include "threading/mutex_auto_lock.h"
 #include "common/c_types.h"
 #include "common/c_internal.h"
 
@@ -108,7 +108,7 @@ class ScriptApiBase {
 	void objectrefGetOrCreate(lua_State *L, ServerActiveObject *cobj);
 	void objectrefGet(lua_State *L, u16 id);
 
-	JMutex          m_luastackmutex;
+	Mutex           m_luastackmutex;
 	std::string     m_last_run_mod;
 	// Stack index of Lua error handler
 	int             m_errorhandler;