test: Add a simple new/delete test for Tox.

This can be used for some static analysis that doesn't currently survive
a full iterate loop, but can possibly survive a new+kill.

auto_tests/tox_new_test.c

@@ -0,0 +1,8 @@
+#include "../toxcore/tox.h"
+
+#include "../toxcore/ccompat.h"
+
+int main(void) {
+    tox_kill(tox_new(nullptr, nullptr));
+    return 0;
+}