Add opt. RAII-isms for destruction, fix thread bug

Thread Bug: Incorrectly using && operator for while
(DqnJobQueue_TryExecuteNextJob(queue) &&
!DqnJobQueue_AllJobsComplete(queue)) causing it to prematurely exit if
the main thread has completed its work before other threads have
completed the remainder. Should be using an || operator, so instead
creating a helper function which encapsulates this functionality.

makefile

@@ -1,3 +1,3 @@
 all: dqn_unit_test.cpp
 	mkdir -p bin
-	gcc -o bin/dqn_unit_test dqn_unit_test.cpp -lm -Wall -Werror
+	g++ -o bin/dqn_unit_test dqn_unit_test.cpp -lm -Wall -Werror