Coroutine debugging tools

[IsaacKhor]

I've been using the coroutine functions, and can't help but notice that debugging coro code is a disaster. Pointers towards doing the following would be good:

• Looking at a coroutine backtrace with the ability to inspect each "stack frame" (inspect local variables, function arguments, etc) (gdb bt/up/down/frame <x>/info locals equivalents)
• Looking at all the pending async tasks (gdb info threads/thread <x> equivalent)

The current co_bt.py script just shows a backtrace without the ability to inspect any of the frames.