Added coverage for multiple init/shutdown.

examples/00-helloworld/helloworld.cpp

@@ -16,6 +16,13 @@ int _main_(int _argc, char** _argv)
 	uint32_t debug = BGFX_DEBUG_TEXT;
 	uint32_t reset = BGFX_RESET_NONE;
 
+	// It's possible to call init/shutdown sequence multiple times inside
+	// the same application if it is necessary. State created between one
+	// init and shutdown doesn't carry over to another.
+	bgfx::init();
+	bgfx::shutdown();
+
+	// Now init for real example.
 	bgfx::init();
 	bgfx::reset(width, height);