Allow customization of the modules that enable strict/warnings.

There are several different ways to do this, but this seemed like the easiest.  Alternatively, you could create a function that adds modules to the strict/warning lists.  That way, you don't expose the internal variables.  On the other hand, a raw variable gives maximum flexibility.

I included a test case, but I found the current test code to be a bit janky.  And the POD has been updated too.