Suggestion: Add the ability to call a user supplied method at regular intervals in loop_forever()

Given that use of loop() is discouraged (and reading the code for loop_forever I can see why) and that it can be tricky to ensure use of loop_start() is thread safe, it would be helpful for loop_forever() to accept an optional argument of a function that, if provided is called regularly to perform any additional functionality that the program needs.

From my limited understanding of the code it looks as though this could be achieved by testing if the function exists and if so calling it just after the call to loop() in loop_forever()