refactor: 💥 q_* UDL renamed to _q_*

We had some fun exploring the STD UDLs for potential collisions,
we have learnt our lesson and know how to proceed.
Now is high time to start behaving and obeying C++ rules.

example/alternative_namespaces/timer.cpp

@@ -13,7 +13,7 @@ int main()
 {
    std::cout << "Simple timer using mpusz/units ...\n";
 
-   auto const period = 0.5q_s;
+   auto const period = 0.5_q_s;
    auto const duration = 10 * period;
 
    timer t;