Remove QueuedReader and fix method cancellation

[tvoinarovskyi]

As I stated in #52 fixing the cancellation issue without removing reader is too hard.
I've gone through the code base. The Reader is responsible for synchronous consumption of frames, but there is No need for that if we just maintain the code correctly:

• Synchroniser.await should be called right after sender.send_* method. At least it should not contain yield from calls in between.

In asyncio we already have the loop, which has a great scheduling machinery, that will guaranty sequential call order.

[tvoinarovskyi]

If it's hard to review for 0.5 we can just set it to be fixed in 0.6.

[coveralls]

Coverage increased (+0.2%) to 96.009% when pulling bc4265f on TarasLevelUp:cancel_methods into 8f55f2f on benjamin-hodgson:master.