[RFC] merge offcputime and offwaketime

I recently made a couple of changes to offcputime.py (#533, #543 and #544). I was going to port them to offwaketime.py when it occurred to me that including the stack of the waking process could be a feature of offcputime.py (that was default off). I'm envisioning something like `parser.add_argument('-w', '--show-wakeup-stack', ...)`.
How do we feel about merging these two tools into one vs maintaining separate tools?
I can take this on if we think it's a good idea.

cc @brendangregg