Add thread safe way of removing multiple handlers at the end of an arbitrary handler fn.
Add thread safe way of removing multiple handlers
at the end of an arbitrary handler fn.

* To remove the current handler return :remove_handler
* To remove an arbitrary handler return [:remove_handlers,
                                         [handle, key]*]
jweather/sonic-pi,jweather/sonic-pi,jweather/sonic-pi,jweather/sonic-pi,jweather/sonic-pi