Consider merging aio and task frameworks

[gdamore]

Originally we had the idea of a general purpose task framework, and that the aio framework could make use of it. However this separation has complicated things a bit, and it would be easier to follow the flows, if we had the entirety of the task framework in the aio framework.

This might allow us to reduce some of the hot locks as well, and in particular I want to break up the aio_lk.

[gdamore]

This is something I'd still like to do, but its tricky to do it, and still obtain any performance benefit.