Initial commit of the async version

[KimiNewt]

Not fully working yet. Some features missing, not tested.
A lot of things were changed, mainly the threads and generators were
changed to coroutines, but the old interface was kept to be backwards
compatible.

[KimiNewt]

Currently only requires further testing.
There is also a problem where the stderr is printed to stdout despite being seemingly redirected to os.devnull. This is similar to the problem we had in #26
@bbayles looking at the issue, you seemed to have an async version already (which I seem to have missed, doh). It's no longer up. Did you solve the stderr issue somehow?

[bbayles]

I don't think I had a problem with the version of subprocess I was using (Py3k+) - maybe try with subprocess32 on Py2.7?

Also look at the -Q option in TShark, perhaps.

[KimiNewt]

Trollius already uses its own subprocess version. I'll check some other things out and otherwise will just use -Q as you suggested.

I think that while the code may be difficult to understand for someone who hasn't done any async programming, it works out rather well while working both asyncly and syncly depending on the situation-- and still allow interactivity.