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/unittest/CMakeLists.txt

@@ -17,6 +17,7 @@ set (UNITTEST_SRCS
 	${CMAKE_CURRENT_SOURCE_DIR}/test_serialization.cpp
 	${CMAKE_CURRENT_SOURCE_DIR}/test_settings.cpp
 	${CMAKE_CURRENT_SOURCE_DIR}/test_socket.cpp
+	${CMAKE_CURRENT_SOURCE_DIR}/test_threading.cpp
 	${CMAKE_CURRENT_SOURCE_DIR}/test_utilities.cpp
 	${CMAKE_CURRENT_SOURCE_DIR}/test_voxelalgorithms.cpp
 	${CMAKE_CURRENT_SOURCE_DIR}/test_voxelmanipulator.cpp