Allow hooks to be added globally after tests are registered

[KyleJune]

Currently this module requires hooks to be registered first before calling describe/it globally.

At the global level this was needed because I need to determine if Deno.test should be called once at the top level with all the hooks and top level test cases being called as steps or if the top level tests should be registered with Deno.test instead. If there is a way to delay calling Deno.test until all test cases are registered using describe/it, I could make the determination right before the tests start running. That would make it possible to call the global level hook functions and describe/it blocks in any order.